BEIRUT – Syria’s top diplomat in London said he could no longer represent the regime and defected Monday, as civilians fled the commercial hub of Aleppo in droves amid 10 days of fierce battles between rebels and government forces.

Britain’s Foreign Office said that Khaled al-Ayoubi, the charge d’affaires, told officials that he wasn’t willing to represent the regime any longer, the latest high-profile defection of a diplomat from Syria over the bloody crackdown on the opposition since March 2011.

Fighting is heating up in Aleppo, Syria’s largest city with 3 million people. The U.N. said 200,000 Syrians have left over the past 10 days as the government trains its mortars, tank and helicopter gunships on the neighborhoods seized by the rebels.