BEIRUT, Lebanon (AP) — At least one person was killed and 28 others wounded early Saturday when a bomb ripped through an apartment building in the northern Lebanese city of Tripoli, security officials said.

The explosion occurred in an area that was the scene of fierce sectarian fighting last week between government and opposition supporters, in which nine people were killed and 44 others wounded.

Saturday's blast was caused by a bomb placed in an elevator in the building in Tripoli's Bab el-Tabaneh district, whose Sunni Muslim residents support the government, said the officials in Beirut and Tripoli. They spoke on condition of anonymity because they were not authorized to speak to the media.

Some of the wounded were in critical condition, the officials said.

The explosion caused heavy damage to the building and nearby buildings, the state-run National News Agency reported. It said the sound of the blast forced hundreds of panicked residents out of their beds and into the street to help rescue efforts.

Shortly after the blast, three people were hit by sniper's fire in the pro-government district, the security officials said. The source of the fire came from the pro-opposition neighborhood, they said.

Sunni Muslim government supporters from the Bab el-Tabaneh district and Alawite followers of the Hezbollah-led opposition in the nearby Jabal Mohsen neighborhood fought last week for two days before the army and police deployed Monday to quell violence.

Despite the army and police presence, tension has been rising between the two sides. About 20 houses in both neighborhoods were torched this week in apparent acts of revenge. Hours before Saturday's bomb blast, two men were wounded when a hand grenade was thrown at the motorbike they were riding in the Alawite district, the officials said.

The violence in the north comes as Western-backed Prime Minister Fuad Saniora struggles to form a national unity Cabinet in line with a peace deal signed in May, which ended an 18-month political crisis that nearly plunged Lebanon into a new civil war.

Located 50 miles north of Beirut, Tripoli is Lebanon's second largest city and is predominantly Sunni Muslim, a majority of which support the government. But it is also home to Alawites, a small offshoot of Shiite Islam that is allied with Syria and the Lebanese opposition, led by the Shiite militant Hezbollah group.

The same area had witnessed heavy fighting last month, when pro-government gunmen and militias loyal to the opposition clashed after Hezbollah militants overran streets in Beirut.