WASHINGTON — President Trump said Thursday night that the United States had carried out a missile strike in Syria in response to the Syrian government’s chemical weapons attack this week, which killed more than 80 civilians.
“Tonight, I ordered a targeted military strike on the air base in Syria from where the chemical attack was launched,” Mr. Trump said in remarks at his Mar-a-Lago estate in Florida. “It is in this vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons.”
Mr. Trump — who was accompanied by senior advisers, including Stephen K. Bannon, his chief strategist; Reince Priebus, his chief of staff; his daughter Ivanka Trump; and others — said his decision had been prompted in part by what he called the failures by the world community to respond effectively to the Syrian civil war.
“Years of previous attempts at changing Assad’s behavior have all failed, and failed very dramatically,” the president said, referring to President Bashar al-Assad of Syria. “As a result, the refugee crisis continues to deepen, and the region continues to destabilize, threatening the United States and its allies.”
Dmitri S. Peskov, a spokesman for President Vladimir V. Putin of Russia, told reporters Friday morning that the strike “deals a significant blow to relations between Russia and America, which are already in a poor state,” according to the news agency RIA.
Mr. Peskov said the strike did nothing to combat international terrorism. “On the contrary, this creates a serious obstacle for building of an international coalition to fight it and to effectively resist this universal evil,” he said. Fighting terrorism was Mr. Putin’s stated goal when he dispatched the Russian military to Syria in September 2015, though its main effect has been to shore up Mr. Assad.
Capt. Jeff Davis, a Pentagon spokesman, said Russian forces had been notified in advance of the strike. “Military planners took precautions to minimize risk to Russian or Syrian personnel located at the airfield,” he said. No Russian aircraft were at the base, military officials said.
“We are assessing the results of the strike,” Captain Davis added. “Initial indications are that this strike has severely damaged or destroyed Syrian aircraft and support infrastructure and equipment at Shayrat airfield, reducing the Syrian government’s ability to deliver chemical weapons.”
The cruise missiles struck the airfield beginning around 8:40 p.m. Eastern time on Thursday, and the strikes continued for three to four minutes.
According to Captain Davis, the missiles were fired from the destroyers Porter and Ross in the eastern Mediterranean.
Talal Barazi, the governor of Homs Province, where the base sits, told Reuters early Friday that ambulances and fire trucks were scrambling to respond to fires there.
Administration officials described the strikes Mr. Trump ordered as a graphic message to the world that the president was no longer willing to stand idly by as Mr. Assad used horrific weapons in his country’s long civil war. To do otherwise, they said, would be to essentially bless the use of chemical weapons by Mr. Assad and others who might use them.
“This clearly indicates the president is willing to take decisive action when called for,” Secretary of State Rex W. Tillerson told reporters in Florida. He said Mr. Trump had concluded after seeing the results of the chemical attack that the United States could no longer “turn away, turn a blind eye.”
“The more we fail to respond to the use of these weapons, the more we begin to normalize their use,” Mr. Tillerson said, a thinly veiled reference to President Barack Obama’s decision to refrain from strikes in 2013.
Mr. Tillerson added that the United States had not informed Mr. Putin about the coming missile strikes and that Mr. Trump had not spoken with the Russian leader in the hours afterward.
The decision to act came with a swiftness that took observers of the new president by surprise. After being briefed on the chemical attack shortly after it occurred, American intelligence agencies and their allies worked quickly to confirm the source of the chemical weapons, administration officials said.
In Washington the next day, the president convened a meeting of senior members of his National Security Council, where military aides presented him with three options. Officials said Mr. Trump peppered them with questions and directed them to focus on two of those options.
On Thursday, after Mr. Trump traveled to Florida for his dinner with President Xi Jinping of China, he convened what officials described as a “decision meeting” with his top national security aides — many of them with him at Mar-a-Lago, and others on secure video screens from Washington.
After what aides called a “meeting of considerable length,” Mr. Trump authorized the missile strikes before starting the dinner with Mr. Xi.
President Trump retaliated against the Assad government for a chemical attack in Syria that killed more than 80 civilians.
“It was important during the president’s deliberations,” said H. R. McMaster, the president’s national security adviser, to weigh the risk of action against the “risk of this continued, egregious, inhumane attacks on innocent civilians with chemical weapons.”
A military official said the attack was at the more limited end of the military options presented to Mr. Trump on Thursday by Defense Secretary Jim Mattis. The official said the strike was intended to send a signal to Mr. Assad about the United States’ intention to use military force if he continues to use chemical weapons.
It was the first time the White House had ordered military action against forces loyal to Mr. Assad.
Mr. McMaster said the missile strikes would not eliminate Mr. Assad’s ability to use chemical weapons, but would degrade it. He said the United States military had specifically sought to avoid hitting what it believes is a facility containing more sarin gas at the airfield.
He said the military had also sought to “minimize risk” to citizens of other countries — specifically Russians — who might have been in the area at the time.
The Pentagon on Thursday night released a graphic showing the flight track of Syrian aircraft as they left the Shayrat field on Tuesday and carried out the chemical attack in the town of Khan Sheikhoun in Idlib Province.