Authorities arrested a senior Pakistani Taliban commander who led the group's network in the key central province of Punjab, where violence has been increasing in recent months, police said Thursday.

The arrest strikes a blow as militants have stepped up their efforts to wage attacks far from their sanctuary in Pakistan's lawless tribal area near the Afghan border in response to a major military offensive there.

Khalil Ullah, whose arrest was announced Thursday, was the mastermind of a market bombing in Punjab's provincial capital, Lahore, on Dec. 7 that killed 49 people, said senior police investigator Chaudhry Shafiq. He declined to say where or when Ullah was arrested.

More than 500 people have been killed in attacks throughout the country since the army launched an anti-Taliban offensive in the South Waziristan tribal area in mid October. The military has secured much of the territory in the area, but operations continue.

Soldiers raided a hospital used by militants in South Waziristan on Thursday, killing five foreign fighters, intelligence officials said. The troops captured 27 militants, 10 of whom were wounded in a gunbattle that broke out during the raid, they said.

It was unclear whether the troops suffered any casualties, the officials said on condition of anonymity because they were not authorized to talk to the media.

Many militants are believed to have fled South Waziristan to avoid the fighting and have been launching attacks in different areas of the country, including a bombing of a Shiite Muslim procession in the southern city of Karachi on Monday that killed 44 people.

On Wednesday, the Pakistani Taliban claimed responsibility for the bombing, a sign the militants may be escalating their war against the state with a rare attack in Pakistan's commercial hub.

Although the teeming city of about 15 million has often been the scene of sectarian, ethnic and political violence, the Pakistani Taliban have rarely claimed responsibility for attacks there. Many analysts believe the group has spared it in the past because its militants used the city as a haven to raise money and to rest.

President Asif Ali Zardari has speculated the motive was to spark sectarian conflict that could complicate the government's battle against the Pakistani Taliban.

Pakistan has a history of violence between extremist elements among its majority Sunni Muslim and minority Shiite communities. Although the Taliban are not known for launching sectarian attacks, they have associations with Sunni militant groups that have targeted minority Shiites, whom they regard as heretical.

It is unclear whether the Taliban carried out the bombing on its own or received help from other militant groups that officials say have a joint goal to destabilize Pakistan.

The bombing sparked rioting that destroyed buildings and thousands of shops in central Karachi, causing millions of dollars in damage. Parts of Bolton Market, the country's largest wholesale market, were still smoldering more than 48 hours after the attack.

Mobs roamed the streets immediately after the blast, setting fire to nearby buildings, firing guns into the air and throwing stones at security forces who had been assigned to protect the procession.

Officials initially blamed Shiites in the procession for the rioting but later said it was a planned conspiracy — a stance that may be intended to temper sectarian tensions.

Sunni religious leaders and politicians in Karachi have called for a strike to protest the attack and ensuing violent rampage. They have urged businesses and public transport companies to shut down Friday, a move that could paralyze the city.