Suicide attacker detonated an explosive-laden vehicle inside a high-security military base, killing 16 soldiers from an elite counterterrorism task force. Pakistan officials vowed to step up its fight against terrorism Friday.
Authorities did not speculate on who was behind the attack, but Islamic militants will be suspected.
Mostly Muslim Pakistan is a key ally of the United States in its campaign against terrorism, and has seen scores of attacks since Sept. 11, 2001, when President Gen. Pervez Musharraf threw his support behind Washington. Hundreds of suspected militants have been killed or detained.
Twenty-nine soldiers were also wounded in the attack late Thursday at Ghazi Tarbela base - about 100 kilometers (60 miles) south of the capital, Islamabad - the headquarters of the quick-reaction counterterrorism commandos.
Musharraf ordered a thorough investigation into how the bomber penetrated security at the facility and rammed his vehicle into a canteen where soldiers were eating, according to a statement on the state-run Associated Press of Pakistan news agency.
"The government will fight the menace of terrorism, extremism and militancy in all its forms and manifestations," Musharraf said.
The attack against Pakistani soldiers came the day visiting U.S. Deputy Secretary of State John D. Negroponte met with Musharraf in Islamabad, and praised his role in the fight on terror.
The slain soldiers belonged to the army's Karar commando group, which has participated in operations against militants in various parts of the country, according to officials, who spoke on condition of anonymity because of the sensitive nature of their jobs.
Army spokesman Maj. Gen. Waheed Arshad, who had suggested Thursday the blast may have been accidentally triggered by a gas canister, confirmed a suicide attacker was suspected.
He said investigations were continuing, but declined further comment.
The Karar force had taken part in the army's July raid against pro-Taliban militants in Islamabad's Red Mosque, which left more than 100 dead and triggered a spate of reprisal attacks against security forces, Geo TV network reported.
Pakistan is under growing U.S. pressure to crack down on Taliban and al-Qaida in its border regions. It reported Wednesday it killed about 40 militants in the North Waziristan tribal region.
In fighting Thursday near Razmak, a town in South Waziristan, army forces repelled repeated militant attacks, and tribesmen informed officials up to 50 rebels died in counter-strikes. Two soldiers were killed and eight wounded, Arshad said.
Fighting between Islamic militants and security forces has been raging across northwest Pakistan since the army assaulted the Red Mosque. Most of the combat has been in the rugged mountains along the Afghan border, where the U.S. fears al-Qaida is regrouping.
The army says it has deployed 90,000 troops in the border region in an attempt to curtail militancy and stop guerrillas from crossing into Afghanistan to attack NATO forces.