UNITED NATIONS (AFP) - UN Secretary General Ban Ki Moon "remains convinced that the use of chemical weapons by any party (in Syria) under any circumstances would constitute an outrageous crime," the United Nations said on Tuesday.

The comment came after Syria's government and opposing rebels on Tuesday each accused each other of using chemical weapons for the first time in two years of unrest in Syria.

Mr Ban and Mr Ahmet Uzumcu, Director-General of the Organisation for the Prohibition of Chemical Weapons, "shared deep concern about the alleged use of chemical weapons in Syria," the UN said in a statement following their conversation.

The two men pledged to "maintain close contact as developments unfold."

UN spokesman Martin Nesirky said that the UN was "aware of the report" that chemical weapons had been used in Syria, but said "we are not in a position to confirm it."

Moscow, a key ally of President Bashar al-Assad, said it had "information" from Damascus that rebels had used chemical weapons, while Washington said there was "no evidence" that the insurgents had staged their first chemical attack and warned it would be "totally unacceptable" for the regime to use such arms.