Syrian government troops clashed with rebels for a second straight day in the northern city of Aleppo, as the intensifying conflict sent thousands of civilians from across the war-torn nation pouring into neighboring Lebanon and Iraq.

Activists described the fighting in Aleppo as some of the fiercest to date in Syria's commercial hub and largest population center. The city has remained largely loyal to President Bashar al-Assad and had been spared the daily bloodshed that has plagued other areas.

Residents said Damascus was largely calm Saturday after days of heavy clashes that left corpses on the streets of the capital.

The United Nations reported that an estimated 30,000 Syrians have crossed into Lebanon since Thursday. Authorities in Iraq say about 1,000 people arrived from Damascus by air, while thousands more people trying to escape the escalating violence arrived from Syria by land.

Turkey has registered more than 43,000 refugees from Syria, but many others are believed to have crossed into Turkish territory without being counted.

An attempt by Western and Arab nations to impose U.N. Security Council sanctions on Syria failed this week after Russia and China vetoed the plan.