A suicide attacker detonated a car bomb at a checkpoint in a northwestern Pakistan town on Saturday, killing at least 20 security forces personnel, officials said.
The attack on the security forces checkpoint took place in Doaba, a town in restive Hangu tribal district, some 70 kilometers (43 miles) southwest of provincial capital Peshawar, an official said, not far from the Afghan border.
"At least 20 security forces members and policemen were killed in the suicide attack," and 10 others were injured, a security official told AFP.
"Most of the casualties are security forces and some policemen have also been killed," the official said, adding that police and military checkpoints were located a short distance from each other.
Another security official said the security forces had intelligence about the possibility of a suicide attack and they were beefing up the checkpoint when the suicide bomber struck.
Earlier, security officials said that five policemen were killed and that the attack occurred as a military convoy passed their checkpoint.
"The attack occurred at 4:10 pm (1010 GMT)," an official confirmed.
Security forces immediately cordoned off the area, which lies close to Pakistan's lawless tribal areas bordering Afghanistan.
There was no immediate claim of responsibility for the attack and police were unable to identify the bomber.
President Asif Ali Zardari, who is in China attending an international economic conference, "condemned the attack and vowed to root out terrorism and extremism from the country," the presidency said in a statement.
Pakistan Prime Minister Yousuf Raza Gilani "strongly condemned" the incident, describing the suicide attack as "a cowardly act of terrorism," his office said in a statement.
The frequent suicide bombings and attacks risk the stability of cash-strapped, nuclear-armed nation.
At an aid meeting in Tokyo on Friday, donor countries pledged $5.28 billion to help stabilise poverty-stricken Pakistan, seen as a frontline state in the war against Islamic extremism.
Pakistani security troops are frequent targets for extremist militants, who oppose the government's role in the US-led "war on terror."
More than 1,500 government forces have been killed by insurgents since 2002.
Much of the violence has been concentrated in northwest Pakistan, where the army has been fighting hardline Taliban and Al-Qaeda extremists who fled the 2001 US-led invasion of Afghanistan.
Taliban warlord Baitullah Mehsud has threatened to launch suicide attacks to avenge missile strikes by US drones targeting Islamist militants in the tribal areas.