The top US military officer has told a Senate committee he believes Russia bombed the humanitarian aid convoy in Syria on Monday, calling it an "unacceptable atrocity".

A 23-lorry convoy has delivered humanitarian aid to a Damascus suburb besieged by government forces, as the UN resumes its aid deliveries to Syria's opposition areas.

US secretary of state John Kerry said yesterday that the evidence of a massive deadly chemical attack last week was “undeniable” and accused the Syrian government of trying to cover it up, signalling the United States was edging closer to a possible military response.

Snipers have fired on the UN convoy carrying a team investigating the use of chemical weapons in Syria, but failed to deter them from their mission today.

The UN weapons team investigating the Syrian regime’s use of chemical weapons has been attacked by sniper fire as it set out in convoy for the area where hundreds of civilians died.