US destroyers based in the eastern Mediterranean launched a barrage of cruise missiles on Syria early Friday morning in retaliation against a suspected chemical weapons attack on civilians blamed on President Bashar Assad.

US officials said 59 Tomahawk missiles targeted the Shayrat Airfield in Homs, from where they believe Syria jets that carried out the Tuesday's attack on Khan Sheikhoun took off. The strike targeted Syrian aircraft, an airstrip and fuel stations, officials said.

The missile strikes are the first time the United States has directly targeted Assad's forces in the six-year war.

The move marks a major escalation in the conflict after US President Donald Trump, who on the campaign trail warned of being dragged into the bloody multi-sided conflict, hinted the United States would retaliate for the suspected chemical attack. 

Trump cites national security

Speaking at his Mar-a-Lago resort, where he is meeting with the Chinese president, Trump said the missile attack was in the United States' "vital national security interest."

The United States must "prevent and deter the spread and use of deadly chemical weapons," he said, adding there was no doubt the Syrian regime carried out a chemical attack on the rebel-held town of Khan Sheikhoun.

The missile strikes raise the risk of confrontation with Russia and Iran, Assad's main backers. It was not immediately clear whether Russian or Iranian forces had been hit.

Russia's Ambassador Vladimir Safronkov had warned earlier that the there could be "negative consequences" if Washington took military action in Syria.

"All responsibility if military action occurs will be on the shoulders of those who initiated such a doubtful tragic enterprise," Safronkov said.