PESHAWAR: A suicide bomber rammed an explosives-laden vehicle into a military checkpoint in Pakistan's troubled northwest on Saturday, killing at least 20 people, officials said.

While militant attacks are spreading across Pakistan, the onslaught remains fiercest near Taliban strongholds along the Afghan border, where al-Qaida fugitives — perhaps including Osama bin Laden — have found sanctuary.

The explosion demolished the checkpoint and severely damaged an adjacent building housing troops and police, said Farid Khan, a senior police official in the nearby town of Hangu.

At least 18 members of the security forces as well as two civilians died, Khan said. More than a dozen other people were wounded, including the local police chief, other officials said.

Prime Minister Yousuf Raza Gilani condemned the attack as a "cowardly act of terrorism" and said the government would use an "iron hand" against terrorists and extremists, his office said in a statement.

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. Suicide 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.