Following a deadly air strike on aid trucks the previous night, the UN humanitarian aid agency has temporarily suspended all convoys in Syria.

Spokesman Jens Laerke, of the Office for the Coordination of Humanitarian Affairs (OCHA), said the temporary suspension of the aid deliveries would hold pending a review of the security situation in Syria.

Mr Laerke said on Monday that the UN aid coordinator had received needed authorisations from the Syrian government in recent days to allow for aid convoys to proceed within Syria.

He said it's "a very, very dark day... for humanitarians across the world".

The attack late on Monday came just hours after the Syrian military declared the week-long US-Russian brokered ceasefire had failed.

The United States said it was prepared to extend the truce deal and Russia - after blaming rebels for the violations - suggested it could still be salvaged.