The main confrontation around the Grand Serail was over in less than two hours. By nightfall, only about 30 protesters were left, many of them young Syrians, vowing to camp there until the government fell. The security forces blocked off all entrances to the Serail with coils of barbed wire about two yards high.

Only minor injuries were reported from the scuffles in Beirut, but there were scattered reports of more violent episodes and Sunni-Shiite tensions elsewhere in Lebanon, including gun battles in the northern city of Tripoli, which has a standing fault line between two adjacent neighborhoods, one primarily Sunni Muslim and the other Alawite, the same main factions arrayed against each other in Syria.

Overnight, The Associated Press said, Sunni and Shiite gunmen clashed in two Beirut neighborhoods and officials reported heavy clashes late Sunday and early Monday in Tripoli and towns between Beirut and the southern city of Sidon. The officials, speaking on condition of anonymity because they were not authorized to talk to the media, said a man was killed in shooting in the Wadi Zayneh area north of Sidon and another person died in the Tripoli clashes. The officials said the clashes wounded at least six people in Beirut and 10 in Tripoli, The A.P. said.

In Damascus, Lakhdar Brahimi, the United Nations and Arab League peace envoy in Syria, met with Mr. Assad to try to arrange a short cease-fire for Id al-Adha, the feast of sacrifice that Muslims around the world will celebrate at the end of this week.

But the difficulty in stopping the violence was accented by a car bomb that went off in the square of Bab Tuma, the gateway to a storied neighborhood in the old city. The Syrian state-run news agency, SANA, put the toll at 13 killed and 29 injured, and published photos of a string of blackened vehicles that it blamed on a “terrorist” attack.

A senior Arab official, moreover, said on Monday the hope for a cease-fire was “weak.”

Ahmed Ben Hilli, deputy secretary-general of the Arab League, told Reuters that the authorities in Damascus “do not show any signs of a real desire to implement this cease-fire.” With Id al-Adha only days away, he said, “we hope the situation changes and the government and opposition respond even a little bit to this door for negotiations.”