The Syrian army says six people were killed in the missile attack, which also caused extensive damage to the air base.

A statement from the army command said it would respond by continuing its campaign to "crush terrorism" and restore peace and security to all of Syria.

The statement described the attack as an act of "blatant aggression", saying it had made the United States "a partner" of Islamic State, the Nusra Front and other "terrorist organisations".

Iran - an ally of Syria - has also condemned the attack, while China's foreign ministry has urged the "relevant parties" to "remain calm".

Bahram Qasemi, a spokesman for Iran's foreign ministry, said the strike was "destructive and dangerous".

"Iran strongly condemns any such unilateral strikes," he said. "Such measures will strengthen terrorists in Syria ... and will complicate the situation in Syria and the region."

China's spokeswoman said it was urgent to prevent any further deterioration in the situation.

She said China supported UN agencies conducting an independent investigation into the Syrian chemical weapons attack to find hard facts that stand the test of history.

"The Syrian issue should be resolved through political means. China hopes the relevant parties remain calm and exercise restraint," she said.