A suicide car-bomber rammed a Pakistani military convoy on Saturday, killing 25 soldiers and police, and two passers-by, police said.
About 65 people were wounded. Pakistani Taliban claimed responsibility for the attack near Kohat, 190 km (120 miles) west of Islamabad.
"The bomber was driving a pick-up truck which he rammed into a convoy passing by a security checkpost," said senior police officer Fareed Khan in the northwestern town of Kohat.
Mr Khan said the death toll could rise because at least seven out of the 65 wounded were said to be in a critical condition.
About eight vehicles in the convoy were destroyed.
President Asif Ali Zardari told aid donors on Friday he would step up the fight against militants and said defeat for nuclear-armed Pakistan would be a defeat for the world.
His nation is a vital US ally in its efforts to stabilise Afghanistan.
A spokesman for Pakistani Taliban chief Baitullah Mehsud said militants would continue its attacks on security forces.
"It was retaliation for the US drone strikes and security forces will have to see more attacks because our people have suffered many losses in the missile attacks," Hakimullah Mehsud said by telephone from an undisclosed location.
The United States, frustrated by an intensifying insurgency in Afghanistan getting support from the Pakistani side of the border, began launching more drone attacks last year.
Since then, about 35 US strikes have killed about 350 people, including mid-level al Qaeda members, according to reports from Pakistani officials, residents and militants.
Pakistan objects to the strikes. Officials say about one in six of the strikes over the past year caused civilian deaths without killing any militants. This fuels anti-US sentiment and complicates the military's struggle to subdue violence.
The government has struggled to come up with an effective strategy to deal with militancy, alternating in different areas between military offensives and peace deals. But the militants have only gained strength.
Mr Zardari, under pressure from conservatives, signed a regulation on Monday imposing Islamic sharia law in the Swat valley to end Taliban violence there.
The strategy of appeasement has alarmed US officials while critics say the government has demonstrated a lack of capacity and will to fight the Taliban and al Qaeda.
Reuters