Syrian government troops and rebels have clashed for a second straight day in the northern city of Aleppo.

Activists say the overnight fighting is some of the fiercest to date in Syria's northern commercial hub.

An activist network – the Local Coordination Committees – says the clashes have caused many residents to flee the area.

On Friday, the U.N. Security Council unanimously approved a 30-day extension of the monitoring mission in Syria, but it remains divided on how to resolve the increasingly bloody conflict.

The 300 unarmed military observers were deployed as part of U.N. envoy Kofi Annan's plan to end a conflict that has killed thousands. But the mission has been viewed as largely ineffective.

The U.S. Ambassador to the United Nations, Susan Rice, said the decision to extend the mission will allow the troops to withdraw safely. She said the U.S. would prefer to see stronger sanctions imposed on Syria, but Russia on Friday again threatened to veto such a resolution.