Syrian troops and opposition fighters were locked in clashes near the Golan Heights in Syria's southern province of Daraa Thursday, a day after rebels abducted 21 UN peacekeepers.

The fighting erupted near the village of Jamlah, about one km from the Israeli-controlled territory, according to the Britain-based Syrian Observatory for Human Rights.

On Wednesday, around 30 gunmen detained 21 Filipino peacekeepers in Jamlah, urging the government to stop bombardment and withdraw troops, according to activists of the "Martyrs of Yarmouk" rebel brigade which had claimed responsibility for the capture.

The captives appeared in several videos and said they were being well-treated by rebels and civilians alike, but no one has given a clue on when they might be freed.

The UN mission have been monitoring a ceasefire line between Syria and the Israeli-occupied Golan Heights for some four decades. The abduction has been a sign that Syria's violence might spread out of its borders, as it nears its second anniversary.

Israel said it would not intervene to negotiate about the release of kidnapped UN soldiers, but will lend a helping hand if needed, according to a senior defense ministry official.

UN Security Council and Secretary-General Ban Ki-moon condemned the abduction and demanded the immediate release of the peacekeepers -- three officers and 18 enlisted men. The Philippine authorities also condemned the act, calling it a "gross violation of international law."

Meanwhile, in Syria's north, President Bashar al-Assad's forces carried out airstrikes against the city of al-Raqqa near the border with Turkey, which had fallen into the hands of rebels a day earlier.

The rebels are believed to have the provincial governor in captive. The seizure of al-Raqqa could be the opposition's biggest victory on the ground since the start of the anti-government movement in March 2011.

However, Syria's Al-Watan daily reported that rebels captured only "several districts" of al-Raqqa, not the whole city.

In the political sphere, the main opposition group, the Syrian National Coalition (SNC), has been mulling to choose a "provisional prime minister" in a meeting scheduled in Turkey's Istanbul on Tuesday.

The planned meeting, due on March 12-13, is also expected to discuss the formation of an interim government to run the "rebel-held territory," according to a SNC statement.

The opposition also aimed to show that it could fill a power vacuum and has the ability to curb chaos if President Assad should be unseated.

Meanwhile, Turkey's main opposition Republican People's Party sent a delegation to the Syria capital of Damascus to meet with Assad in an apparent display of support for the embattled administration.

The delegation expressed "the Turkish people's rejection of interfering in Syria's internal affairs and keenness for establishing good neighborly relations," the Turkish media reported.

The UN said some 70,000 people have been killed in Syria's two-year-old violence.