The firing of 59 cruise missiles at an air base controlled by Syrian president Bashar al-Assad has created "dangerous unpredictability", according to Alex Salmond.

The SNP MP, who is the party's spokesman on foreign affairs, says the US must develop a strategy to end the conflict in the Middle Eastern state.

US president Donald Trump ordered the aerial assault on the al-Shayrat air base after US intelligence showed it was used to launch a chemical weapons attack on a rebel heled town, Khan Sheikhun, on Tuesday.

Two American navy ships, USS Porter and USS Ross, fired the Tomahawk missiles from the Mediterranean Sea at around 2.40 am UK-time.

Reacting to the air strike, Salmond said: "The overnight cruise missile strikes by the USA against a Syrian regime air base are no substitute for a policy towards ending the conflict.

"Attacking a chemical weapons base can be justified in international law but in itself it provides no solutions.

"Such strikes should take place only after detailed examination and assessment of the storage facility and the delivery mechanism."

Salmond continued: "They should also be part of a collective effort to place the use of chemical weapons and nerve agents beyond the pale of conflict and crucially they should also be part of a considered strategy to bring this ruinous multi-layered Syrian civil war to an end.

"In this case the cruise missile strike seems to dramatically reverse the previous stance of the Trump administration which was to partner Russia and tolerate Assad.

"Thus, there is now further and dangerous unpredictability introduced into a conflict of which America is now at the centre, both in confronting Assad and with troops on the ground among the forces gathering for the assault on the last Daesh stronghold of Raqqa."

Salmond said the US president has a "political interest" in "distancing himself from Russia".

The Russian government has criticised the missile strike and say the Assad regime was not responsible for the chemical weapons attack.

UK Labour leader Jeremy Corbyn has condemned the attack and said it "risks escalating the war in Syria still further".

The UK Government welcomed the missile strike.

A Downing Street spokesman said: "The UK Government fully supports the US action, which we believe was an appropriate response to the barbaric chemical weapons attack."