A homicide car bomber attacked an army convoy at a checkpoint in northwest Pakistan on Saturday, killing at least 27 people near another emerging militant stronghold within striking distance of the Afghan border.

A deputy of Pakistan's top Taliban leader took responsibility for the bombing near the town of Hangu and said more would follow until the U.S. ends missile attacks into Pakistan's tribal areas.

Prime Minister Yousuf Raza Gilani condemned the assault as a "cowardly act of terrorism" and said the pro-Western government would use an "iron hand" against terrorists and extremists.

While militant attacks are spreading across Pakistan, the onslaught remains fiercest near the Afghan frontier, where Al Qaeda fugitives — possibly including Usama bin Laden — have found sanctuary.

The explosion Saturday damaged about a dozen army trucks and jeeps as well as a police station at the checkpoint, said Farid Khan, a senior police official in Hangu.

At least 25 members of the security forces and two civilians died, Khan told The Associated Press by phone from a hospital near the scene. Another 62 security personnel and three civilians were wounded, including the local police chief, other officials said.

Khan said the convoy was about to leave the checkpoint when the bomber exploded his vehicle.

The attack was claimed by Hakeemullah Mehsud, a Taliban commander who vowed earlier this month to carry out two homicide attacks a week to press for the withdrawal of Pakistan troops from the border region and for an end to CIA missile strikes.

"We are meeting our pledge. ... We will intensify our attacks if the drone strikes in the tribal areas do not stop," Mehsud told AP by telephone from an undisclosed location.

Pakistan is under intense international pressure to crack down on an increasingly integrated array of Islamist extremist groups blamed for bloody attacks in Afghanistan, Pakistan and India.

Donors including the U.S, Japan and Saudi Arabia on Friday pledged more than $5 billion to shore up Pakistan's shaky economy and pay for schemes to alleviate poverty and bolster its security forces — twin tracks in a longer-term drive to dry up support for extremism.

Assaults this year in the capital, Islamabad, and on the Sri Lanka cricket team and a police academy in the eastern city of Lahore have fanned fear that militants are expanding across the country and could soon destabilize the state.

The checkpoint hit Saturday is near the Orakzai tribal region, which has emerged in recent months as a major Taliban base. Homicide bombers have targeted community leaders who have sought to rally local tribes against the militants.

An apparent U.S. missile strike reportedly killed 14 suspected militants in Orakzai on April 1, the first such attack in the area since unmanned CIA aircraft stepped up their assault on targets in the tribal belt last year.

The pro-Western government is also calling for and end to the missile strikes, arguing that while they may have killed several militant leaders, they fan anti-American sentiment and help militant groups attract recruits.

Saturday's was the fifth homicide blast in Pakistan so far this month, and the deadliest since 48 worshippers were killed in a mosque in Khyber tribal region in late March.

Hakeemullah Mehsud, a deputy to Pakistani Taliban leader Baitullah Mehsud, had previously claimed responsibility for a homicide attack in the capital on April 4 that killed eight paramilitary troops.