Last Updated 1:07 p.m. ET
(CBS/AP) BEIRUT - Syria's top diplomat in London defected Monday, Britain's Foreign Office reported.
Khaled al-Ayoubi, the charge d'affaires, told officials that he wasn't willing to represent the regime of President Bashar Assad any longer.
The latest high-profile defection of a diplomat from Syria comes as thousands of civilians flee the nation's largest city, Aleppo, amid fierce battles between rebels and government forces.
The United Nations said 200,000 Syrians have fled Aleppo since intense clashes began 10 days ago.
The government forces turned mortars, tank and helicopter gunships against rebel positions Monday, pressing ahead with a counter-offensive to wrest back control of neighborhoods taken by rebels in Syria's largest city and commercial hub.
"I am extremely concerned by the impact of shelling and use of tanks and other heavy weapons on people in Aleppo," Valerie Amos, the top U.N. official for humanitarian affairs, said in a statement late Sunday. "Many people have sought temporary shelter in schools and other public buildings in safer areas," she added. "They urgently need food, mattresses and blankets, hygiene supplies and drinking water."
Amos said U.N. agencies and the Syrian Red Crescent are working together on supplying those affected by the fighting all over the country with blankets and humanitarian supplies, but many remain out of their reach because of the combat.
"It is not known how many people remain trapped in places where fighting continues today," she warned. Aleppo is Syria's largest city and commercial hub with about 3 million inhabitants.
Correspondent Clarissa Ward, who recently traveled with rebel forces in Syria, said Monday that "rebel forces are feeling very emboldened, particularly after the huge battles that have been taking place in Damascus and in Aleppo, the political and economic beating hearts of the regime. So they are feeling emboldened.
"They now also have huge swaths of territory, particularly in the north, but they are still outgunned and outmanned by the regime forces.
To watch Clarissa Ward's report click on the video player below.
The problem rebels now face, said Ward, "is trying to move between the various pockets of territory, the islands that they hold, because the main arteries that connect the primary cities and those highways and freeways are still very much under the control of government forces. Trying to move between them, open up supply lines is a very lengthy and dangerous process.
Ward said that, despite reports that weapons having been flowing across the Turkish border from Saudi Arabia and other Gulf countries, the rebels said they are receiving very little in the way of weapons, and only light weapons at that. "From what we saw, it was still fighting with AK-47s, rocket-propelled grenades," Ward said. "We saw a very small amount of anti-aircraft weaponry. But certainly they are still far, far outgunned by the regime's forces."
Fleeing residents have described to The Associated Press incessant shelling, shortages of food and gasoline and soaring black market prices for everyday staples. They scurry through streets against a backdrop of gunfire and climbed onto any form of transportation available to escape, including trucks, cars and even heavily laden motorcycles.
U.S. Defense Secretary Leon Panetta said late Sunday that the use of heavy weapons, particularly helicopters, is just another nail in Assad's coffin. He spoke during a stopover in Tunisia as he kicked off a Mideast tour expected to focus heavily on the unfolding crisis in Syria.
Syrian state media reported late Sunday that the army had "purged" Aleppo's southwestern neighborhood of Salaheddine and inflicted "great losses" upon the rebels in one of the first districts they took control of in their bid to seize the city.