Beirut, Lebanon ? Pro-Syrian President Emile Lahoud on Saturday canceled plans to attend an Arab summit, citing “exceptional circumstances” after a car bomb rocked a Christian neighborhood in Beirut, injuring nine people in a blast that raised the specter of renewed sectarian violence.

The explosion in north Beirut, the Mediterranean coastal city that was ravaged by 15 years of civil war that ended in 1990, complicated efforts to restore stability in Lebanon.

It came even as Syrian troops finally were withdrawing under global pressure, a month after the assassination of Prime Minister Rafik Hariri in a massive bombing that killed 17 others.

The deepening political crisis also prompted Lahoud, a staunch supporter of Syria’s 29-year involvement in Lebanon, to call for dialogue between the pro- and anti-Syrian camps. But the opposition quickly rejected his overtures, demanding an international inquiry into Hariri’s Feb. 14 assassination and the ouster of top Lebanese security officials. Some said Lahoud must step down.

Investigators searched the rubble of a bombed building for clues in the attack just after midnight. The explosion, in addition to the nine casualties, devastated an eight-story apartment building in the largely Christian New Jdeideh neighborhood, blowing off the fronts of some structures and gouging a seven-foot-deep crater in the pavement. Cars parked nearby were damaged as were shops. Windows were shattered in buildings several blocks away.

The motive for the attack was not known, but it played to concerns among some Lebanese that pro-Syrian elements might resort to violence to prove the need for a continued presence by Damascus forces.

Opposition leader Walid Jumblatt warned there could be more car bombs and assassination attempts but urged calm.

“Car bomb messages do not threaten our national unity,” he said in a speech to supporters at his mountain palace of Mukhtara, southeast of Beirut.

The military announced stricter measures against any security violators, saying in a statement: “The army will not allow that freedom of expression be abused in order to harm security and stability,” a reference, perhaps, to massive pro- and anti-Syrian demonstrations that have clogged central Beirut in recent days.

Security officials, speaking on condition of anonymity, said the blast was caused by a time-bomb placed under a car that belonged to a Lebanese-Armenian resident in the damaged eight-story building. The whereabouts of the vehicle’s owner were not known.

Earlier, witnesses said the car attempted to stop in front of a bingo hall, but security guards asked its driver to move along. The driver then parked the car down the road. Minutes later it exploded.