Syria's charge d'affaires in London, Khaled al-Ayoubi, resigned his post on Monday, according to the British Foreign Office. He was Syria's most senior diplomat in the British capital after President Bashar al-Assad withdrew his ambassador to London in March.

"Mr. al-Ayoubi has told us that he is no longer willing to represent a regime that has committed such violent and oppressive acts against its own people, and is therefore unable to continue in his position," the Foreign Office said in a statement. "His departure is another blow to the Assad regime. It illustrates the revulsion and despair the regime's actions are provoking against Syrians."

The diplomat had been in the Syrian service since 2001, first serving as consul in Greece from 2003 to 2008. The Foreign Office in London also used its statement to "urge others around Bashar al-Assad to follow al-Ayoubi's example."

Turkish officials reported on Monday that a dozen Syrian police officers, including the deputy chief for the western city of Latakia, had left their posts and fled to Turkey overnight.

Hundreds of thousands flee Aleppo

According to the United Nations as many as 200,000 people have fled fighting in Syria's second city, Aleppo in recent days. Opposition forces control much of Aleppo and have been in pitched battles against government troops sent to regain control.

"I am extremely concerned by the impact of shelling and use of tank and other heavy weapons on people in Aleppo," UN Undersecretary-General for Humanitarian Affairs Valerie Amos said in a statement. "Many people have sought temporary shelter in schools and other public buildings in safer areas. They urgently need food, mattresses and blankets, hygiene supplies and drinking water."

Amos also warned that it was hard to tell how many people were trapped in areas of the city where the fighting was most fierce. Aleppo, usually the commercial capital and second city of Syria, is home to well over 2 million people.

Rebel forces, spearheaded by the Free Syrian Army (FSA), launched an attempt to overrun Aleppo on July 20 - later saying they had been partially successful. Aleppo has been the scene of fierce fighting ever since. The north-western city, far from the capital Damascus in the south-west, is also close to the Syrian border with Turkey. Some have said that rebel fighters might be seeking to establish a northern stronghold close to the FSA's nominal headquarters in Turkey.

msh/mz (AFP, AP, Reuters)