Beating their chests with hands, thousands of minority Shiite Muslims attended a mass funeral Saturday for those killed in a pair of bombings in Pakistan's largest city.

At least 33 people died and 170 others were wounded in Karachi on Friday when suspected Sunni militants targeted a bus carrying Shiite worshippers and then attacked a major hospital treating victims of the first bomb, said government spokesman Jamil Soomro.

Karachi has a history of religious violence between Shiite and Sunni Muslims, and the city has been tense in recent weeks due to clashes between rival political parties that have left dozens dead.

The chaos in Karachi has added to the instability tearing at nuclear-armed Pakistan, which has been challenged by Al Qaeda and Taliban violence and whose help the U.S. needs to shore up its war effort in neighboring Afghanistan.

Paramilitary spokesman Maj. Aurang Zeb said security forces were on maximum alert at the funeral in the Malir area of the southern port city. Many businesses were observing a strike over the attacks.

Witnesses said about 7,000 mourners attended the funeral.

Although no group claimed responsibility, Pakistan is home to Sunni extremist groups with a history of attacking Shiites.

In late December, 44 people died when a bomb ripped through a Shiite procession in the city to mark the anniversary of the death of revered Shiite figure Imam Hussein.

Friday's blasts coincided with Arbaeen, the final day of the annual 40-day mourning period for Hussein. The first bomb targeted a bus carrying Shiite worshippers, most of them women and children. The bomb was attached to a motorcycle and detonated as the bus drove to an Arbaeen procession.

Two hours later, the second bomb exploded outside the entrance to the emergency ward at Jinnah Hospital, which was packed with victims and relatives of those killed and wounded in the earlier attack.

Although Pakistan's Sunnis and Shiites generally live in peace, extremists on both sides often target each other's leaders and places of worship.

Also Saturday, a bomb attached to a motorcycle went off as a security convoy passed through a busy area in the southwestern city of Quetta in Baluchistan province, wounding seven civilians, police official Mohammed Sadiq said.

No one claimed responsibility, but authorities have blamed Baluch nationalists for previous such attacks aimed at security forces.

Nationalists in the impoverished southwestern province have waged a violent campaign for years to demand more autonomy and a greater share of income from the area's natural resources for its residents.