Inspectors from the UN are heading to the site of an alleged chemical-weapons attack near Damascus, the Syrian capital, amid a ceasefire in the area approved by the Syrian government and the armed rebels in the country.

Monday's planned visit follows calls from Western powers for military action to punish Syria for the incident and statements from Washington and its Western allies claiming that potential evidence in the area has probably been destroyed by heavy government shelling over the past five days.

The six-car convoy of chemical weapons experts wearing blue UN body armour was accompanied by a car of security forces as well as an ambulance.

They said they were headed to the rebel-held area known as eastern Ghouta, where activists say rockets loaded with poison gas killed hundreds of people early on Wednesday.

The UN announced on Sunday that the Syrian government and rebels had agreed to observe a ceasefire during the visit.

It said the rebels and government were responsible for the safety of the inspectors on the ground.

The agreement between the Syrian foreign minister and the head of the UN delegation to let the experts in was reached on Sunday.

The agreement "is effective immediately and it will allow UN delegation to investigate allegations of using chemical weapons on August 22 in Damascus suburbs", Syrian state TV reported.

The alleged chemical-weapon attack in Ghouta on Wednesday killed 355 people and wounded hundreds more, according to the aid group Medecins Sans Frontieres.

'Unprecedented aggression'

On the diplomatic front, Francois Hollande, the French president, told his US counterpart Barack Obama over a phone conversation on Sunday that "everything was consistent" with the conclusion that Damascus was behind the attack.

"The two presidents agreed to stay in close contact to arrive at a joint response to this unprecedented aggression," Hollande's office said.

For his part, William Hague, UK foreign secretary, has said that any evidence of a chemical attack may have been destroyed.

"The fact is that much of the evidence could have been destroyed by that artillery bombardment," he said on Sunday.

The government of Bashar al-Assad has denied responsibility for Wednesday's attack and blamed the rebels fighting Assad's forces of the same.

The rebels have held the regime forces responsible for the attack.

The alleged chemical weapons attack has spurred calls for global action against Assad's government.

The US government has been under mounting pressure to act, with President Barack Obama having defined the use chemical weapons as a "red line' for Syria.

As the Syrian National Council, an opposition umbrella organisation, called on major powers to intervene in Syria, Obama met senior security officials on Saturday to consider US options on how to respond to the crisis.