BEIRUT (AP) — Lebanese gangs backing the regime in Damascus smashed storefronts belonging to Syrian merchants on Wednesday and a powerful clan claimed it was holding more than 20 Syrians captives as the civil war across the border stirred tensions in this fragile Arab nation.

The flurry of violence came in response to Syrian rebels seizing a Lebanese man suspected of links to Shiite militant group Hezbollah, a strong supporter of Syrian President Bashar Assad's regime along with Shiite power Iran.

It exposed the inherent volatility in Lebanon, which is a patchwork of groups backing Assad and others siding with those trying to bring him down.

The tensions took on a distinctly sectarian tone. Syrian rebels are predominantly Sunni whereas Assad and his inner circle are dominated by Alawites, an offshoot of Shiite Islam.

Sunni Gulf powers Saudi Arabia, Qatar and the United Arab Emirates, sensing the possibility for a quick escalation in sectarian violence, called on all their citizens in Lebanon to leave immediately. They cited fear of abductions by Shiites angry over the strong Saudi and Qatari backing for the Syrian rebels. Lebanon is a popular summer destination for Gulf residents trying to escape the searing heat.

Syria was deeply enmeshed in Lebanon's own 15-year civil war, which ended in 1990. Syria dominated Lebanon for decades, but pulled out its tens of thousands of troops there in the face of mass street protests over the 2005 bombing that killed anti-Syrian Lebanese Prime Minister Rafik Hariri. A U.N.-backed tribunal later indicted four members of Hezbollah.

The battles for control of Syria now threaten to reopen Lebanon's rivalries. Gunfights have erupted between pro- and anti-Assad groups over the past months, including a May clash in the northern city of Tripoli that left eight people dead.

The wave of hostage-taking across Lebanon also included a Turkish businessman, who appeared on pro-Syrian television saying he was visiting Lebanon as a sales executive. Turkey is also a major opponent of Assad's regime.

"All these events are Syrian-related. ... The fear is that it develops into wider abductions," said Ibrahim Bayram, an expert on Shiite affairs who writes for Lebanon's An-Nahar newspaper.

In Syria, rebels have stepped up hostage-taking as a tactic to rattle Assad and his allies outside the country. In May, Syrian rebels captured 11 Lebanese Shiites shortly after they crossed from Turkey on their way to Lebanon. Earlier this month, rebels abducted 48 Iranians near the capital Damascus.

On Tuesday, a rebel video purported to show captive Hassane Salim al-Mikdad — a member of a formidable Shiite clan — flanked by gunmen. He said he is a member of Hezbollah and was sent to Syria to fight with Assad regime forces.

Hezbollah denied al-Mikdad is a member and his family claimed he has been living in Syria for more than a year.

But the al-Mikdad clan swiftly followed through with threats to grab their own captives in retaliation. Abu Ali al-Mikdad, a relative, told reporters in Beirut that they abducted "more than 20 Syrians," including a senior member of the rebel Free Syrian Army. Later, the family announced they were also holding the Turkish businessman.

The Beirut-based TV station Al-Mayadeen aired a video purporting to show two of the abducted Syrians who said they are members of the rebel army. One of them identified himself as Capt. Mohammed and said his job was to supply the rebels with arms and fresh fighters.

"I call them (the Free Syrian Army) upon to free the prisoners they are holding because they are innocent," said one of the two captured men shown on TV who identified himself as Maher Hassan Rabih.

The al-Mikdad family is a powerful Shiite Muslim clan that originally comes from the eastern Bekaa Valley, an area where state control is limited. Like most tribes in this area, they have their own militia support. Their reach also extends deep into the capital.

A south Beirut neighborhood with strong al-Mikdad ties, Rweis, is often avoided by outsiders who fear any possible offense that could put them at odds with the clan. Shiite backers of the al-Mikdads also vandalized more than 35 Syrian-run stores in another district, Hay El-Selom, and warned them not to reopen without their approval, according to security officials.

Hours later, Shiite protests blocked the airport road, causing passengers to walk to try to reach their flights. An Associated Press reporter saw burning tires and gunmen on the road.