A powerful explosion late Monday rocked a shopping center and hotel in the Zalka neighborhood in north Beirut, injuring at least three people and causing extensive damage, security officials said.

Heavily armed Lebanese soldiers cordoned off the area, punching and hitting journalists to keep them back.

Two workers could be seen helping a black-clad, veiled woman down the glass-covered front stairs of the Promenade Hotel. She appeared shaken but not injured. Shattered glass and plaster filled the hotel lobby, but no residents were hurt.

Brig. Gen. Darwish Hobeika (search), Lebanon's Civil Defense Corps commander, told Lebanese Broadcasting that two people were lightly injured and one Civil Defense rescuer was hurt.

The explosion shattered the windows of several apartment buildings and blew shutters off dozens of luxury boutiques in the neighborhood. Black smoke billowed high in the night sky, but there was no fire.

Aluminum siding and roofing in the shopping center buckled. The state-run National New Agency estimated the explosion was caused by 45 pounds of TNT.

Security forces were seen rounding up several suspects, including five men with their hands tied behind their backs who were taken to a military vehicle.

Zalka Mayor Michel Murr (search) told the Lebanese Broadcasting Corp. the bomb was placed in an open area between the Centre Moussa shopping center and the Promenade hotel, which was packed with tourists. He said none was hurt.

Zalka, on the Mediterranean coast, is a mixed residential and commercial area on a main street that leads to Lebanon's Christian heartland. The area has several cafes — including a Starbucks coffee shop — and restaurants and other nightspots that were full of patrons.

The explosion was the latest in a string of bombings that have killed or wounded politicians and other prominent figures in Lebanon since the February assassination of former Prime Minister Rafik Hariri (search), an attack that rattled Lebanon's political and security foundations.

Bombs also have targeted commercial and industrial centers. The bomb that killed Hariri took 20 other lives, and explosions since then have killed at least six people, including a prominent politician and an anti-Syrian journalist. More than 50 people, including Lebanon's defense minister, have been injured.

The most recent explosion occurred July 23, just hours after Secretary of State Condoleezza Rice (search) made a brief, unannounced visit to Beirut. The blast in a busy Christian neighborhood wounded 12.

Hariri's assassination on a Beirut street, which many people blamed on Syria, triggered anti-Syrian protests at home and international pressure that eventually ended three decades of Syrian domination of Lebanon with the withdrawal of the Syrian army.

The latest bombing was sure to intensify political tension between the anti-Syrian Lebanese, who won parliamentary elections in May and June, and pro-Syrian politicians.

The tensions are fueled in part by the unfinished U.N.-mandated investigation into Hariri's assassination and media leaks about alleged suspects and their involvement.

At the United Nations Monday, Undersecretary-General for Political Affairs Ibrahim Gambari (search) said U.N. investigators are making progress in their investigation into Harari's assassination but need more time to complete their work.

The investigation, which formally began June 16, is led by a German prosecutor, Detlev Mehlis, who is expected to return to New York in September to report to the U.N. Security Council.