A military official said Friday that investigator suspected there had been a man who had helped a suicide bomber who killed 16 soldiers in the dining hall of a Pakistani commando base.
Security officials initially said that Thursday's blast at the Ghazi Tarbela base, about 100 kilometers (60 miles) south of the capital, Islamabad, was the work of an attacker driving an explosives-laden vehicle.
But a senior army officer told The Associated Press on Friday that survivors said they had seen a man enter the busy dining room and blow himself up, killing 16 troops and wounding another 29.
"Now we know for sure that the suicide attacker entered the dining hall," said the official, who sought anonymity because he is not authorized to speak on the record. "It was not possible without the support from some insider, or someone who had access."
Evidence that Islamic militants possibly linked to al-Qaida can penetrate the high-security surrounding elite army units could shake faith in Pakistan's ability to combat extremism.
Meanwhile, army spokesman Maj. Gen. Waheed Arshad confirmed only that the blast was a suicide attack. He declined to comment on how the bomber managed to reach his target.
The base houses the Special Operations Task Force raised after the Sept. 11, 2001 attacks in the United States and which officials say has participated in numerous operations against Islamic militants.
Commandos from the force reportedly took part in the 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.
Visiting U.S. Deputy Secretary of State John D. Negroponte met with President Gen. Pervez Musharraf Thursday and praised Pakistan's commitment to fighting terrorism.
However, militants have met stepped up military action since the July mosque raid with a spate of attacks on security forces along the Afghan border and suicide attacks in some of its main cities.
The military has reported killing some 90 militants during the past two days in battles in the South Waziristan frontier region. Up to ten soldiers have also died.
On Friday, militants freed 11 soldiers kidnapped three days earlier in the northwestern town of Bannu, said Hamza Masood, a police official.
However, insurgents are still holding some 260 soldiers seized in South Waziristan on Aug. 30.