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Russia has threatened to boost its air defences in Syria and cut communication with US forces after President Donald Trump ordered cruise missiles strikes on a Syrian regime military airbase in Homs province.

Moscow - a key military and political ally of Damascus - has ramped up its rhetoric against Washington on Friday morning following the strikes on the Shayrat airbase in central Syria.

It called the attacks "an aggression under fake pretence" and that the US strikes were "comparable to 2003 Iraq invasion".

In a more immediate response, Russia said it would suspend a deal on joint-communication with the US military commanders to avoid potential clashes in Syrian airspace.

US jet planes are striking Islamic State group and al-Qaeda linked militants in Syria, while Russia is backing Damascus and targeting opposition towns and villages.

Moscow announced that it would ramp up air defences in Syria in an attempt to show a tough line on the US actions.

"[This is to] protect Syria's most sensitive infrastructure, a complex of measures will be implemented in the near future to strengthen and improve the effectiveness of the Syrian armed forces' air defence system," said Kremlin spokesman Igor Konashenkov.

Despite the apparant surprise, the US says it gave Russian troops based in Syria prior warning before the attack.

This allowed Russian troops to leave the central Syrian base quietly and potential avoid a hugely compromising situation for the two world powers. The attack does appear to have left Moscow red-faced.

Shayrat airfield was believed to be the launch-pad for a regime chemical attack on a Syrian village earlier this week.

The base was left with severe damage making it effectively inoperable, while up to 14 regime jet fighters - and perhaps including the one that launched the devastating sarin attack - were destroyed in the attack.

There were no reports of more high-tech and modern weaponry being being at the airfield when the Tomahawk missiles struck.

Analysts believe that the attack on Shayrat was a limited response by the US to the regime chemical attack on Khan Sheikhun which left up to 100 civilians dead.

Russia has meanwhile called for an emergency UN meeting, but its usual veto-wielding ally, China, has been more mooted in its response to the missile strikes.