The Pentagon said initial indications are that the strike "severely damaged or destroyed Syrian aircraft and support infrastructure and equipment at" the Shayrat Airfield.

The missiles were fired from two U.S. destroyers in the eastern Mediterranean and hit the airbase at approximately 8:40 p.m. Eastern Time (1245GMT). Aircraft, hardened aircraft shelters, petroleum and logistical storage, ammunition supply bunkers, air defense systems, and radars were targeted, the Pentagon said.

"Every precaution was taken to execute this strike with minimal risk to personnel at the airfield," according to Capt. Jeff Davis who said the strike was a "proportional response to Assad's heinous act". 

In addition to storing planes, Davis said Shayrat was used to store chemical weapons. 

Separately, a U.S. official said strikes are completed unless a decision is made for more action. 

The base is reportedly home to hardened fortifications used to house Syrian aircraft and it is unclear if the jets that were stationed there were moved before the U.S. carried out its attack. 

Russia, which has propped up government of Syrian President Bashar al-Assad, was informed of the military action prior to the strikes for deconfliction purposes. 

"U.S. military planners took precautions to minimize risk to Russian or Syrian personnel located at the airfield," Davis said. 

President Donald Trump told reporters the strikes are in the “vital national security interest” of the U.S. and urged “civilized nations” to join Washington in “seeking to end the slaughter and bloodshed in Syria.

"Using a deadly nerve agent, Assad choked out the lives of innocent men, women and children," he said. "Even beautiful babies were cruelly murdered in this very barbaric attack." 

Trump said there is no dispute Assad's forces used banned chemical weapons and he urged international action to cease the bloodshed and "terrorism of all kinds and all types.

Secretary of State Rex said Russia has failed to live up to an agreement signed in 2013 to eliminate chemical weapons in Syria. 

“Either Russia has been complicit or Russia has been incompetent in its ability to deliver,” he said.

The strikes Thursday night are the first taken against Assad's forces since Trump assumed office at the end of January. They are a sharp departure from his reaction to a similar chemical attack in 2013 when he urged then President Barack Obama not to take action. 

Trump said earlier this week that Monday's attack on the outskirts of Khan Shaykhun in Idlib province crossed "a lot of lines" and is an "affront to humanity". 

He said it caused him to rethink his long-standing views on Syria and Assad.

Syrian state media called the strikes Thursday a "U.S. act of aggression". 

The military action has drawn praise from top Republican lawmakers John McCain and Lindsey Graham who said it sent an “important message” the U.S. would “no longer stand idly by as Assad, aided and abetted by Putin’s Russia, slaughters innocent Syrians with chemical weapons and barrel bombs”.

But not all members of the president’s party support the move. Rand Paul tweeted that Trump needs congressional authorization for the strikes “as required by the Constitution”.

Anadolu Agency