Britain's Foreign Office says Syria's chief diplomat in London has defected, making him the latest top official to quit in protest of Syria's bloody crackdown against the opposition.

The foreign office said Monday that Charge D'affaires Khaled al-Ayoubi informed it that he would no longer represent President Assad's government.

Also Monday, Syrian troops and rebels continue to clash in the northern city of Aleppo, with each side claiming victory.

The government said it had overrun the district of Salahhedine and inflicted great losses against the rebels. But rebel forces said no government troops were in the neighborhood and that fighting is ongoing.

In New York, United Nations Secretary-General Ban Ki-moon said he is extremely concerned about the impact the shelling and heavy weapons are having on civilians. He also called on Syria to promise not to use chemical weapons under any circumstances.

Syrian Foreign Minister Walid al-Moallem has vowed the rebels in Aleppo will be defeated.