Washington (Reuters): US President Donald Trump said on Thursday he ordered missile strikes against a Syrian airfield from which a deadly chemical weapons attack was launched, declaring he acted in America’s “vital national security interest” against Syrian President Bashar al-Assad.

Sharply escalating the US military role in Syria , two US warships fired dozens of cruise missiles from the eastern Mediterranean Sea against the airbase controlled by Assad’s forces in response to the poison gas attack on Tuesday in a rebel-held area, US officials said.

Facing his biggest foreign policy crisis since taking office in January, Trump took the toughest direct US action yet in Syria’s six-year-old civil war, raising the risk of confrontation with Russia and Iran, Assad’s two main military backers.

US officials insisted they informed Russian forces ahead of the missile attacks and that there were no strikes on sections of the base where Russians were present. But they said the administration did not seek Moscow’s approval.

“Years of previous attempts at changing Assad’s behavior have all failed and failed very dramatically,” Trump said from his Florida resort, Mar-a-Lago, where he was attending a summit with Chinese President Xi Jinping. Trump ordered the strikes just a day after he pointed the finger at Assad for this week’s chemical attack, which killed at least 70 people, many of them children, in the Syrian town of Khan Sheikhoun. The Syrian government has denied it was behind the attack.

Fifty-nine Tomahawk missiles were launched from the USS Porter and USS Ross around 8:40 p.m. EDT, striking multiple targets – including the airstrip, aircraft and fuel stations – on the Shayrat Air Base, which the Pentagon says was used to store chemical weapons.

“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,” said Pentagon spokesman Captain Jeff Davis.

The attacks spurred a modest flight to safety in global financial markets, sending yields on safe-haven US Treasury securities to their lowest since November. Stocks weakened in Asia and US equity index futures slid, indicating Wall Street would open lower on Friday. Prices for oil and gold both rose, and the dollar slipped against the Japanese yen.

Syrian state TV said that “American aggression” had targeted a Syrian military base with “a number of missiles and cited a Syrian military source as saying the strike had “led to losses.”

Trump said: “Syrian dictator Bashar al-Assad launched a horrible chemical weapons attack on innocent civilians. … Tonight I ordered a targeted military strike on the airfield in Syria from where the chemical attack was launched.”