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

The Britain-based Syrian Observatory for Human Rights says government forces were shelling several neighborhoods in Aleppo, and 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.

Also Tuesday, Syrian opposition figures meeting in Cairo said they will begin forming a transitional government in exile.

U.N. Secretary-General Ban Ki-moon said Monday 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.

U.N. humanitarian chief Valerie Amos says an estimated 200,000 people have fled Aleppo over the past few days – the city at the center of the rebel and government's fight for control.