Every time a patient is stretchered into the Athbah field hospital south of Mosul, doctor Sultan prays it isn't his sister or brother.

Syrian rebels on Friday welcomed a US strike on a government airbase, but urged additional action, with one powerful faction saying a single strike was "not enough."

The US attack on the Shayrat base in central Syria was Washington's first military action against the regime in the six-year civil war.

Britain's government "fully supports" US strikes against a Syrian air base launched after a suspected chemical attack on Tuesday, a spokesman said.

"The UK government fully supports the US action, which we believe was an appropriate response to the barbaric chemical weapons attack launched by the Syrian regime," the spokesman said in a statement on Friday.

Iranian Foreign Minister Mohammad Javad Zarif said on Friday that a US missile strike on a Syrian airbase was based on "bogus" chemical weapons allegations. 

Washington "resorts to military force over bogus CW (chemical weapons) allegations: 1st in 2003 and now in Syria," he tweeted.

Turkey on Friday welcomed a US missile strike on a Syrian regime airbase in retaliation for a suspected chemical attack, calling for a no-fly zone in the country to prevent further bloodshed.

Turkish President Recep Tayyip Erdogan's spokesman Ibrahim Kalin said the strike against the Sharyat airbase in Homs, northern Syria, was "a positive response" to the "war crimes" of the regime of President Bashar al-Assad.

Syrian President Bashar Assad bears "sole responsibility" for the US strike on a regime airbase, German Chancellor Angela Merkel and French President Francois Hollande said in a joint statement on Friday.

"After the chemical weapons massacre of April 4 on Khan Sheikhun in northwestern Syria, a military installation of the Syrian regime was destroyed by a US air strike last night," the statement, issued after a morning phone call, said. 

Israeli Prime Minister Benjamin Netanyahu said he supports the "strong and clear message" sent by a US strike on neighbouring Syria on Friday in retaliation for a suspected chemical attack.

The Israeli military said it had been informed in advance of a massive cruise missile strike on a Syrian airbase, the first US operation against the Damascus regime in six years of civil war.

Saudi Arabia said Friday that it "fully backs" a US air strike on a Syrian government airbase in retaliation for a suspected chemical weapons attack on a rebel-held town.

"Saudi Arabia fully supports the US military operations against military targets in Syria, which were a response to the regime's use of chemical weapons against innocent civilians," a foreign ministry official told the state SPA news agency.

Moscow slammed the US strike on a Syrian airbase Friday as "aggression against a sovereign state", and suspended a bilateral agreement to help avoid clashes in the skies over the war-torn country.

"President Putin considers American strikes on Syria aggression against a sovereign state in violation of international norms, and under an invented pretext," said the statement by the Kremlin press service posted on the official website.

The U.S. military strike on a Syrian airbase has caused several deaths, said the governor of Homs province where the Shayrat base is located.