MASNAA, Lebanon – Syrian security forces killed as many as 20 Lebanese gunmen who were fighting alongside rebels in Syria on Friday, raising tensions amid mounting fears that the Syrian civil war is enflaming the region.

The Lebanese security officials said the gunmen were killed as they tried to enter the Syrian town of Tal Kalakh, near the Lebanese border.

The Lebanese gunmen were Sunni Muslims, as are the vast majority of Syria’s rebels. Syrian President Bashar Assad — along with his most elite troops — belong to the Alawite sect, an offshoot of Shiite Islam.

Lebanon is particularly vulnerable to getting sucked into the conflict in Syria. The countries share a complex web of political and sectarian ties and rivalries that are easily enflamed. Lebanon has been on edge since the uprising in Syria against Assad began in March 2011, with deadly clashes between pro- and anti-Assad Lebanese groups erupting on several occasions.

The deaths came as rebels have tried to close in on the Syrian capital of Damascus.

On Friday, Syrian soldiers fought rebels in and around the capital as Internet and most telephone lines were blacked out for a second day. But the intense battles around the country’s international airport appeared to have calmed.

The airport road had reopened by Friday and the Syrian Civil Aviation Agency said the airport was operating “as usual.” A day earlier, fighting forced the closure of the road and airlines canceled international flights to Damascus.

The communications blackout has raised fears of an explosion of fighting outside the public gaze. The Internet has been a key tool of activists over the course of the Syrian conflict, which started 20 months ago and has left more than 40,000 people dead, according to activists.

Syrian authorities previously have cut Internet and telephones in areas ahead of military operations. On Friday, some land lines were working sporadically.