Beirut: A powerful Shiite Muslim clan in Lebanon on Thursday claimed to have abducted more Syrian nationals and vowed further kidnappings in retaliation for the seizure of a family member by rebels in Syria this week, as Syria's civil war threatened to break open violent rivalries in its neighbor Lebanon.

The wave of kidnappings raises the dire scenario that the battle for control over Syria will ignite tensions in Lebanon, a country with an explosive sectarian mix, with deep divisions between pro- and anti-Syrian factions and with its own history of civil war.

On Wednesday, Shiite supporters of the family clan went on a rampage in a Beirut neighbourhood, vandalizing dozens of Syrian-run stores, and then blocked the road to the airport, setting tires on fire and wandering the road with guns. The road was only reopened early Thursday morning. In past months, gunfights have erupted between pro- and anti-Syrian groups in Lebanon, including a May clash in the northern city of Tripoli that left eight people dead.

Armed members of the Al Mikdad clan, a powerful Shiite family with tribal connections in eastern Lebanon's Bekaa Valley where revenge killings are common, said Wednesday they had kidnapped more than 20 Syrian nationals and a Turk in Lebanon in retaliation for the abduction of their relative, Hassane Salim Al Mikdad, who was captured in Syria this week.

Rebels who kidnapped Al Mikdad claimed he was a member of the Shiite militant group Hezbollah, a staunch supporter of President Bashar Assad's regime. Hezbollah and his family deny this.

Maher Al Mikdad, a family spokesman, warned Thursday that the family would kill some of its captives - starting with the Turk - if Hassane were harmed.

"I warn them, if anything happens to Hassane, we will kill the Turkish hostage we have and many others. But we will start with the Turks," Al Mikdad told The Associated Press.

He said the clan has snatched more Syrians and warned that it would go on with further kidnappings until their clansman is released. He could not give an exact number but said the clan was now holding more than 20 captives.

The wave of hostage-taking prompted Gulf countries to call on all their citizens in Lebanon to leave immediately. Sunni regional powerhouses Saudi Arabia and Qatar, who back the Syrian rebels, were the first, followed by the United Arab Emirates, Bahrain and Kuwait.

Al Mikdad backed off Thursday from an earlier threat to abduct Gulf nationals and said only Syrians and Turks would be targeted.

"Our problem is with the Syrians who have abducted our son and Syrian opponents of the region," he said. "And why Turkey? Because Turkey is an operation theater for the Free Syrian Army," he added.

Turkey shelters thousands of Syrian refugees along with the leadership and members of the Free Syrian Army rebel group.

The conflict in Syria has a sharply sectarian tone. The rebels are predominantly Sunni, whereas President Bashar Assad and his inner circle come mainly from the Alawite sect, an offshoot of Shiism. Similarly, Lebanon has had long rivalries between its own Sunni and Shiite communities. Throughout Syria's conflict, Lebanese Sunnis have largely been sympathetic to the Syrian rebellion, while Hezbollah - the main Shiite political power - has backed Al Assad.

Fighting between Syrian government troops and rebels continued Thursday in various parts of Syria, particularly in the north where large swathes of territory have fallen under the control of opposition fighters.

International watchdog Human Rights Watch said Thursday that Syrian government airstrikes on a residential neighbourhood in the rebel-held northern town of Azaz a day earlier killed over 40 people and wounded at least 100 others including many women and children.

The strikes leveled the better part of a poor neighborhood and sent panicked civilians fleeing for cover. So many were wounded that the local hospital locked its doors, directing residents to drive to the nearby Turkish border so the injured could be treated on the other side.

Reporters from The Associated Press saw nine bodies in the bombings' immediate aftermath, including a baby.

Human Rights Watch, which investigated the site of the bombing two hours after the attack, put the number at over 40.

"This horrific attack killed and wounded scores of civilians and destroyed a whole residential block," said Anna Neistat, the group's acting emergencies director. "Yet again, Syrian government forces attacked with callous disregard for civilian life."

HRW said two opposition Free Syrian Army facilities in the vicinity of the attack might have been targets of the Syrian aircraft, but none were damaged.

The bombing of Azaz, some 50km north of Aleppo, shattered the sense of control rebels have sought to project since they took the area from President Bashar Al Assad's army last month. Azaz is also the town where rebels have been holding 11 Lebanese Shiites they captured in May. On Wednesday, Lebanese media reported conflicting reports on their fate, but it was unclear whether they had been affected by the bombing.

Also on Thursday, Syrian state-run television said government troops freed three journalists from the pro-regime Al-Ikhbariya channel who were seized last week by rebels while covering violence in a Damascus suburb.