Security officials say fresh clashes have broken out in northern Lebanon between supporters and opponents of Syrian President Bashar Assad's regime.

The fighting in the northern Lebanese city of Tripoli is a spillover from Syria's civil war.

The Lebanese officials say two people were killed and 17 were wounded on Friday as gunmen from a Sunni district opposed to Assad battled fighters from a neighbouring Alawite area populated by supporters of the Syrian president.

The officials say automatic rifles and rocket-propelled grenades are being used. They spoke on condition of anonymity in line with regulations.

A Lebanese satellite dish operator working for Sky News Arabia, Hussein Nahle, was wounded by sniper fire on Friday, while covering the fighting in Tripoli, northern Lebanon. A Canadian female journalist, who was not immediately identified, was also injured.

The latest round of fighting first erupted on Monday. At least 15 have been killed in the city this week and more than 100 have been wounded.

In Syria, government forces used artillery and rocket launchers on targets in a suburb of Damascus for a third day on Friday, killing at least 21 people, activists say.

An opposition activist told Reuters several bodies are trapped in destroyed buildings and civilians in the Sunni working-class community of Daraya, just southwest of the capital, are trying to flee toward Damascus.

Northwest of Damascus, the town of Zabadani came under heavy shelling on Friday, according to an amateur video posted on the internet.

A government warplane bombed an apartment building in eastern Syria, killing at least 21 people as the regime fought to claw back ground lost to rebel fighters in the area who have made significant advances in the city, activists said.

The air raid on Mayadin, a city in Deir el-Zour province near the Iraqi border, occurred after rebels gained control of a key checkpoint on a bridge over the Euphrates River there, local activist Abu Omar al-Deery said.

The British-based Syrian Observatory for Human Rights said 21 people, including 12 women and a child, were killed in the airstrike. Al-Deery put the death toll at 23. The figures and details could not be independently confirmed due to tight controls over the media in Syria.

Refugees flee to Turkey

Meanwhile, officials in Ankara say more than 3,500 people have entered Turkey from Syria over the past 24 hours.

Turkey's Disaster and Emergency Management Directorate says it was one of the highest daily refugee flows since the uprising in Syria last year.

The agency says there are now 78,000 Syrian refugees sheltering in Turkey.

More than 200,000 Syrians have entered the neighbouring countries of Lebanon, Turkey, Iraq and Jordan to escape the fighting, the UN High Commissioner for Refugees says.

More than 140,000 of them are in Jordan.