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The United States fired 59 Tomahawk cruise missiles at Syria overnight in response to what it believes was a chemical weapons attack that killed more than 100 people.

At least six people were killed, Syria claimed, but the Pentagon said civilians were not targeted and the strike was aimed at a military airfield in Homs.

All but one of the missiles hit their intended target, one U.S. military official told NBC News. The other missile failed.

The strike completed a policy reversal for President Donald Trump — who once warned America to stay out of the conflict — and drew angry responses from Damascus and its main ally, Russia.

The missiles were launched from the USS Ross and the USS Porter in the Mediterranean Sea toward Shayrat Airfield. American officials believe it was used by the government of Syrian President Bashar Assad to carry out a strike on Tuesday involving chemical weapons that resulted in the deaths of more than 100 people.

"Assad choked out the lives of helpless men, women and children," Trump said in remarks from Mar-a-Lago, his family compound in Palm Beach, 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."

The president also called on other countries to end the bloodshed in Syria.

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U.S. officials told NBC News that aircraft and infrastructure at the site were hit, including the runway and gas fuel pumps. Navy Capt. Jeff Davis, a spokesman for the Defense Department, said initial assessments showed that the airfield was severely damaged, reducing Syria's capability to deliver chemical weapons.

The strike provoked an angry response from Russia, which is backing the Assad regime in its six-year civil war against a patchwork of rebel factions and other groups, including ISIS.

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Both regime and rebel forces have committed repeated war crimes, according to a United Nations report last month, with airstrikes by Russian and Syrian jets in particular "claiming hundreds of lives and reducing hospitals, schools and markets to rubble."

A Russian Defense Ministry spokesman disputed the effectiveness of the strike, telling state media that only 23 of the 59 missiles had hit their target.

Syria's military said the U.S. attack violated "all international laws and customs" and that it made America a "partner" of ISIS "and other terrorist organizations." It also condemned the White House for acting "without knowing the truth about what occurred and without identifying those responsible" for the chemical attack.

While the Syrian government condemned the U.S. strike, armed rebel group Ahrar Al Sham told NBC News it welcomed "any U.S. intervention through surgical strikes that would deter the Assad regime capabilities to kill civilians and shorten the suffering of our people."

The Syrian Observatory for Human Rights, a U.K.-based monitoring group, said that Khan Sheikhoun, the town where the chemical attack took place, was bombed again Friday by an unidentified warplane.

Related: Trump: Why I Launched a Missile Attack on Syria

A White House official said more than two dozen members of Congress were briefed by administration officials on the missile strike. Vice President Mike Pence returned to the White House after having gone home for dinner Thursday evening and monitored the events from the Situation Room, officials said.

Trump was in Florida for a meeting with Chinese President Xi Jinpeng. Defense Secretary James Mattis, Secretary of State Rex Tillerson and national security adviser H.R. McMaster traveled to Florida with him.

"We feel that the strike itself was proportional, because it was targeted at the facility that delivered this most recent chemical weapons attack," Tillerson told reporters.

"There was a thorough examination of a wide range of options, and I think the president made the correct choice and made the correct decision," Tillerson said.

Related: Rebel Forces, Some in Congress Praise Strike on Syrian Airfield

Tillerson and Nikki Haley, the U.S. ambassador to the U.N., have bluntly blamed Syria for the chemical weapons attack, whose victims included at least 25 children.

"We have a very high level of confidence that the attacks were carried out by aircraft under the direction of Bashar al-Assad's regime, and we also have very high confidence that the attacks involved the use of sarin nerve gas," Tillerson said.

A map shows the location of Shayrat Airfield in Syria, the site of U.S. missile strikes overnight Thursday. Google Maps

He said there were no executive-level communications with Russian President Vladimir Putin before the missile strike but confirmed U.S. officials had "multiple conversations" with the Russian government in accordance with military "deconfliction" agreements.

Photos: Rescuers Treat Dozens in Syria Chemical Attack

The unilateral action came after Haley told the U.N. Security Council on Wednesday: "When the United Nations consistently fails in its duty to act collectively, there are times in the life of states that we are compelled to take our own action."

Only a week earlier, she had told the U.N. that removing Assad from power was no longer America's priority.

Sen. Marco Rubio welcomed the strike and said regime change should now be a focus. He said Trump should now work with other countries "to create alternatives to the Assad regime," he told NBC's TODAY.