WASHINGTON — The United States and European allies launched strikes on Friday against Syrian research, storage and military targets as President Trump sought to punish President Bashar al-Assad for a suspected chemical attack near Damascus last weekend that killed more than 40 people.
Britain and France joined the United States in the strikes in a coordinated operation that was intended to show Western resolve in the face of what the leaders of the three nations called persistent violations of international law. Mr. Trump characterized it as the beginning of a sustained effort to force Mr. Assad to stop using banned weapons.
“These are not the actions of a man,” Mr. Trump said of last weekend’s attack in a televised address from the White House Diplomatic Room. “They are crimes of a monster instead.”
While he has talked as recently as last week about pulling American troops out of Syria, he vowed to remain committed to the goal of preventing further attacks with deadly poisons. “We are prepared to sustain this response until the Syrian regime stops its use of prohibited chemical agents,” Mr. Trump said.
The strikes, carried with ship-based cruise missiles and manned aircraft, targeted three facilities associated with Syria’s chemical weapons arsenal, including a scientific research facility around Damascus, a chemical weapons storage facility around Homs alleged to be used for sarin gas and a nearby command post, the Pentagon said.
The Syrian Observatory said the Syrian Army’s 4th Division and Republican Guard was among the targets.
Residents of Damascus, the capital, woke to the sounds of multiple explosions shaking the city before the dawn call to prayer. The city and the hills are surrounded by military facilities, and it appeared that these were among the first targets.
Syrian state television said government air defense systems were responding to “the American aggression” and aired video of missiles being fired into a dark night sky. It was not clear if they hit anything. It reported that 13 missiles had been shot down by Syrian air defenses near Al-Kiswa, a town south of Damascus.
The targets were chosen to minimize the risk of accidentally hitting Russian troops stationed in Syria, according to Gen. James F. Dunford Jr., the chairman of the Joint Chiefs of Staff.
Defense Secretary Jim Mattis told reporters at the Pentagon on Friday night that the strike was completed and was designed as a one-night operation. “Right now this is a one-time shot and I believe it has sent a very strong message to dissuade him to deter him from doing it again,” he said.
Mr. Trump called on Syria’s patrons in Russia and Iran to force Mr. Assad to halt the use of poison gas in the seven-year-old civil war that has wracked his country.
“To Iran and to Russia I ask: What kind of a nation wants to be associated with the mass murder of innocent men, women and children?” he said. “The nations of the world can be judged by the friends they keep. No nation can succeed in the long run by supporting rogue states, brutal tyrants and murderous dictators.”
The strikes risked pulling the United States deeper into the complex, multisided war in Syria from which Mr. Trump only last week said he wanted to withdraw. They also raised the possibility of confrontation with Russia and Iran, both of which have military forces in Syria to support Mr. Assad.
In choosing to strike, it appeared that Mr. Trump’s desire to punish Mr. Assad for what he called a “barbaric act” — and make good on his tweets promising action this week — outweighed his desire to limit the American military involvement in the conflict, at least in the short term.
The strikes marked the second time that Mr. Trump has attacked Syria to punish the government after it was accused of using chemical weapons. The White House had sought to craft a response that would be more robust than the attack in April 2017, when the United States fired 59 Tomahawk cruise missiles at a Syrian air base that was back in use a day later.
While France and Britain joined the United States in retaliating for the suspected chemical attack in the town of Douma outside Damascus last Saturday, Germany refused to take part, even though Chancellor Angela Merkel called the use of chemical weapons “unacceptable.”
Prime Minister Theresa May of Britain said Syria had left the allies no choice. “This persistent pattern of behavior must be stopped — not just to protect innocent people in Syria from the horrific deaths and casualties caused by chemical weapons but also because we cannot allow the erosion of the international norm that prevents the use of these weapons,” she said.
But she also emphasized the limits of the operation’s goals, reflecting the reluctance in London as well as Washington to become too immersed in the fratricidal war in Syria.
“This is not about intervening in a civil war,” she said. “It is not about regime change. It is about a limited and targeted strike that does not further escalate tensions in the region and that does everything possible to prevent civilian casualties.”
British defense officials said four Royal Air Force Tornado GR4s participated in the strike, launching Storm Shadow missiles at a military facility about 15 miles west of Homs where they said Syria was believed to keep chemical weapon precursors stockpiled in violation of the Chemical Weapons Convention.
Early reaction to the strikes from Capitol Hill appeared to break down along party lines, with Republicans expressing support for the president and Democrats questioning whether Mr. Trump has a well-thought-out strategy for what happens after the military action is over.
“President Trump’s decision to launch airstrikes against the Syrian government without Congress’s approval is illegal and — absent a broader strategy — it’s reckless,” said Senator Tim Kaine, Democrat of Virginia, who has long argued that presidents should request permission from Congress before taking military action.
Representative Nancy Pelosi of California, the House Democratic leader, said that “one night of airstrikes is not a substitute for a clear, comprehensive Syria strategy.”
Representative Steve Scalise of Louisiana, the House Republican majority whip, wrote in a statement: “President Trump is right to assert that the Assad regime’s evil acts cannot go unanswered.”
The missiles struck Syria shortly after 4 a.m. local time on Saturday. A fact-finding mission from the Organization for the Prohibition of Chemical Weapons was to begin investigating the incident on Saturday in Douma, which had been held by rebels before the suspected attack. The mission’s job was only to determine whether chemical weapons had been used, not who had used them.
Medical and rescue groups have reported that the Syrian military dropped bombs that released chemical substances during an offensive to take the town. A New York Times review of videos of the attack’s aftermath, and interviews with residents and medical workers, suggested that Syrian government helicopters dropped canisters giving off some sort of chemical compound that suffocated at least 43 people.
On Friday, American officials said they had intelligence implicating the Syrian government. “We have a very high confidence that Syria was responsible,” said Sarah Huckabee Sanders, the White House press secretary. She said Russia was “part of the problem” for failing to prevent the use of such weapons.
At the United Nations, Nikki R. Haley, the American ambassador to the world body, accused the Syrian government of using banned chemical arms at least 50 times since the country’s civil war began in 2011. State Department officials said the United States was still trying to identify the chemical used on April 7.
President Emmanuel Macron of France on Thursday cited proof that the Syrian government had launched chlorine gas attacks. The same day, the British Cabinet authorized Prime Minister Theresa May to join the United States and France in planning strikes against Syria.
Leaders in Syria, Iran and Russia denied that government forces had used chemical weapons, and accused rescue workers and the rebels who had controlled Douma of fabricating the videos to win international sympathy.
On Friday, Maj. Gen. Igor Konashenkov, a spokesman for the Russian Defense Ministry, said images of victims of the purported attack had been staged with “Britain’s direct involvement.” He provided no evidence.
Karen Pierce, Britain’s ambassador to the United Nations, called those allegations “bizarre” and “a blatant lie.”
Mr. Mattis had sought to slow down the march to military action as allies compiled evidence of Mr. Assad’s role that would assure the world the strikes were warranted. Mr. Mattis also raised concerns that a concerted bombing campaign could escalate into a wider conflict between Russia, Iran and the West.
Before the strikes, the United States had mostly stopped aiding Syria’s rebels, like those who were in Douma, who want to topple Mr. Assad’s government. The Pentagon’s most recent efforts in Syria have focused on the fight against Islamic State militants in the country’s east, where it has partnered with a Kurdish-led militia to battle the jihadists. It is the roughly 2,000 American troops there that Mr. Trump has said he wants to bring home.
In his televised address on Friday night, Mr. Trump sought to repeat his desire to disentangle the United States from the Middle East at some point. “It’s a troubled place,” he said. “We will try to make it better, but it is a troubled place. The United States will be a partner and friend, but the fate of the region lies in the hands of its own people.”
Russian forces and Iranian-backed militias also are deployed around Syria to help fight the rebellion — including the Islamic State and other extremist groups — that has surged against Mr. Assad since the conflict started more than seven years ago.
Last year’s American attack on Syria came after a chemical attack on the village of Khan Sheikhoun killed scores of people. Mr. Trump ordered a cruise missile strike against the Al Shayrat airfield in central Syria, where the attack had originated. The base was damaged but Syrian warplanes were again taking off from there a day later.
Still, the response set Mr. Trump apart from President Barack Obama, who declined to respond with military force after a chemical weapons attack in August 2013 killed hundreds of people near Damascus, even though Mr. Obama had earlier declared the use of such weapons a “red line.”
Mr. Obama ultimately backed off a military strike and reached an agreement with Russia to remove Syria’s chemical weapons arsenal. That agreement was said to have been carried out, although a series of reported chemical attacks since have raised doubts about its effectiveness.
Both American presidents have sought to keep United States involvement in Syria focused on the battle against the Islamic State, and not on toppling Mr. Assad or protecting civilians from violence.
The question now for Mr. Trump is whether his intervention against Mr. Assad will make it harder to keep the United States from slipping deeper into the Syrian war.