Syria gave the green light on Sunday for United Nations inspectors to carry out a probe into the alleged use of chemical weapons near Damascus, the foreign ministry announced.

"An agreement was concluded today (Sunday) in Damascus between the Syrian government and the United Nations during the visit of the UN high representative for disarmament, Angela Kane, to allow the UN team lead by professor Aake Sellstroem to investigate allegations of chemical weapons use in Damascus province," a ministry statement said.

The agreement "is effective immediately," it added.

The United Nations and the Syrian government "are to agree on the date and time of the team's visit to the sites on which there has been an agreement," the ministry said.

It said the deal was struck in a meeting between Kane, whose organisation has had a 20-member team of inspectors on the ground in Syria since August 18, and Foreign Minister Walid Muallem.

"Syria is ready to cooperate with the inspection team to prove that the allegations by terrorist groups (rebels) of the use of chemical weapons by Syrian troops in the Eastern Ghouta region are lies," Muallem was quoted as telling Kane.

Opposition leaders said Friday that UN inspectors would have "unfettered" access to areas under rebel control such as Eastern Ghouta on the outskirts of Damascus to investigate the use of chemical weapons.

Doctors Without Borders has said 355 people died last week of "neurotoxic" symptoms, after the opposition claimed regime forces unleashed chemicals east and southwest of Damascus last Wednesday causing more than 1,300 deaths.

The regime has denied the charges and in turn accused the rebels of using chemical arms.

The UN team arrived in the Syrian capital last week to begin a hard-won mission which UN officials originally said would last two weeks and cover three sites.

The mission had been repeatedly delayed amid differences with President Bashar al-Assad's regime over the scope of the probe into the alleged use of chemical arms in the 29-month civil war.

But the Syrian government insists it has nothing to hide.

Under its original mandate, the team was expected to investigate Khan al-Assal, near Aleppo, where the government says rebels used chemical weapons on March 19, killing at least 26 people, including 16 Syrian soldiers.

The opposition says government forces carried out the attack.

Damascus had called for a UN probe in March but insisted it focus solely on Khan al-Assal. Ban, however, pressed for broader access and investigation of other sites as well.