The convoy of UN inspectors heading to the site of a suspected chemical attack in Ghouta has been hit multiple times by fire from unidentified snipers, according to the UN.

No casualties were reported as the vehicle came under sniper attack in Damascus' buffer zone.

"The first vehicle of the chemical weapons investigation team was deliberately shot at multiple times by unidentified snipers," said UN spokesman Martin Nesirky.

The Syrian regime blamed "terrorists" for sniper fire aimed at UN inspectors, according to state TV.

The Syrian government and rebels agreed to a ceasefire to allow the inspectors to collect evidence in the Damascus eastern outskirts of Ghouta.

The 20-member convoy is reportedly making a detour to a government checkpoint to change their vehicle.

The experts will take soil, blood, urine and tissue samples for laboratory testing.