A roadside bomb hit a bus taking Pakistani navy employees to work in Karachi on Thursday, killing five people in the third such attack this week and just days after the army chief claimed to have "broken the backbone" of militants.
Within hours of the bombing, the Pakistan Taliban, the country's deadliest militant group, claimed responsibility for the latest Karachi explosion.
The series of attacks in the country's largest city and economic heart show the determination and reach of al-Qaida-linked extremist networks despite American-backed Pakistani army offensives against their main bases in the northwest close to the Afghan border.
Clashes Thursday in the northwest involving security forces, militants and tribesmen killed 29 people, nearly all suspected insurgents, a government official said.
The early morning blast in Karachi mangled the bus and damaged nearby buildings. Four of the dead were sailors, while the fifth was a passer-by, said navy spokesman Salman Ali and Seemi Jamali, a doctor at the city's Jinnah Hospital. Five people were wounded.
Taliban spokesman Ahsanullah Ahsan said the bombing targeted the navy because it is part of the Pakistani military, which backs Washington in battling terrorism, and was carried out by "our men."
"We are attacking the Pakistan army as it is supporting America against us," he told The Associated Press in a telephone call from an undisclosed location.
On Tuesday, remote-controlled blasts 15 minutes apart in different parts of Karachi ripped through two navy buses, killing four navy personnel. The Taliban also claimed responsibility for those two attacks, and warned of more unless the army stopped its campaigns in the northwest.
Karachi is home to 18 million people and is the economic center of Pakistan. It is far from the northwest, but has not been spared the Islamist violence wracking the country over the last four years. The Pakistani navy is based in the city, which is on the Arabian Sea.
The army has launched several offensives in the northwest, but bombings against government and security force targets, as well as indiscriminate attacks on public places, have continued. The Pakistani Taliban have little direct public support, but their identification with Islam, strong anti-American rhetoric and support for insurgents in Afghanistan resonates with some.
Last Saturday, Pakistani army chief Gen. Ashfaq Parvez Kayani told graduating cadets that their force had "broken the backbone" of the militants. Those comments followed American criticism of the army campaign, which has struggled to hold border areas it has retaken from the insurgents.
The clashes Thursday occurred along the border between Pakistan's Kurram and Orakzai tribal regions, both of which are near Afghanistan and have been the focus of army operations against the Taliban.
Government official Amin Khan said a group of militants fought pro-government tribesmen in the Marandi area. Five militants and two tribesmen died in the clash.
Security troops then used artillery and airstrikes against several alleged militant positions in the area, killing 22 suspected militants.
The figures are nearly impossible to verify independently because access to the area is restricted.
Associated Press writers Ishtiaq Mahsud in Dera Ismail Khan, Rasool Dawar in Peshawar and Hussain Afzal in Parachinar contributed to this report.