Death toll from Syria chemical attack rises to 1,300 - activists

France harshly condemned the attacks staged on civilians in the Syrian capital, Damascus.

British Foreign Secretary William Hauge also called on the Syrian government to allow "immediate access" for the UN team investigating allegations of chemical weapons use.

"I am deeply concerned by reports that hundreds of people, including children, have been killed in airstrikes and a chemical weapons attack on rebel-held areas near Damascus,"  said Hague.

"These reports are uncorroborated and we are urgently seeking more information. But it is clear that if they are verified, it would mark a shocking escalation in the use of chemical weapons in Syria.

"Those who order the use of chemical weapons, and those who use them, should be in no doubt that we will work in every way we can to hold them to account. The UK will be raising this incident at the UN Security Council."

Led by Swedish arms expert Ake Sellstrom, the investigations into the alleged use of chemicalweapons will be limited in three areas, including a March attack in the Aleppo suburb of Khan al-Assal.

UN Secretary General Ban Ki-moon had said on Tuesday that, the expert team would conduct its activities in the country for up to 14 days and that could be extended upon mutual consent, as agreed with the Syrian government. 

Ban also urged full access for the expert team to the sites where the chemical weapon attacks allegedly happened. 

"Let me state again clearly that, if confirmed, the use of chemical weapons by any side under any circumstances must be held accountable and would constitute an international crime," he said.