The sources said a local newspaper had received a telephone call from someone claiming to speak on behalf of al Qaeda and declaring that a security target would be bombed in Beirut in retaliation for the arrest last month of 13 group members.

The explosion occurred some three hours later at around 2 A.M.Beirut time, outside the Fakhreddine Barracks in Ramlet al-Baida district of the capital, shattering windows in nearby buildings.

The sources earlier said the blast was caused by a car bomb but they later said it had been caused by an explosive charge near or under the car.

Lebanon has been rocked by more than a dozen explosions in the past 12 months, the largest of which was a truck bomb that killed former Prime Minister Rafik al-Hariri and 22 others in Beirut on February 14.

A U.N. inquiry has implicated senior Syrian security officials and their Lebanese allies in the murder. Three anti-Syrian politicians and journalists have been killed and two wounded since in separate smaller explosions.

The Lebanese authorities last month said they arrested 13 members of al Qaeda and sources say they had been setting up a network for the group in the country.

The group had been believed to have recruited Lebanese and Palestinian refugees to fight U.S.-led forces in Iraq under theleadership of Abu Moussab al-Zarqawi, the sources said. But in recent months there have been indications that the group was stepping up its activities in Lebanon.

Zarqawi has claimed responsibility for a Katyusha rocket attack against northern Israel from south Lebanon in late December. But though Lebanese security sources believe pro-Syrian Palestinian guerrillas were behind that attack, they say Zarqawi's willingness to take credit for it showed he might have an agenda in Lebanon.

Update -1: Here are some pictures of the blast scene, courtesy of AP:

Lebanese inspectors collect evidence from the scene.

Lebanese army soldiers and security officers gather at the scene where a bomb placed at the wall of a military barracks exploded

Lebanese security officers stand guard at the scene of the blast

Photo: Ramlet el Baida beach
Source: Reuters, Ya Libnan