Syrian opposition activists have reported widespread clashes Tuesday, including continued fighting in the country's largest city, Aleppo.

The Britain-based Syrian Observatory for Human Rights said government forces were shelling several neighborhoods in Aleppo, and that soldiers were clashing with rebels in the city.

The Observatory, whose reports from witnesses inside the country cannot be confirmed because of restrictions on foreign media, said President Bashar al-Assad's forces were also shelling parts of Deraa province and carrying out raids there.

Activists said fighting also took place in several areas of the capital, Damascus, and in Homs province.

United Nations Secretary-General Ban Ki-moon said Monday that he is extremely concerned about the impact the shelling and heavy weapons is having on Syrian civilians.

He also called on Mr. Assad to promise not to use chemical weapons under any circumstances.

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

The foreign office said Charge D'affaires Khaled al-Ayoubi informed it that he would no longer represent President Assad's government.