Pakistani troops have been battling Taleban fighters near the border
Eight Pakistani soldiers have been killed in a suicide bomb attack on a security base near the border with Afghanistan, officials have said.
The bomber drove his vehicle into a convoy leaving the base in Wana, the main town in the north-western province of South Waziristan, they added.
Correspondents say the restive tribal area is considered a haven for al-Qaeda and Taleban-linked militants.
Troops have been deployed to combat the militants, but attacks have continued.
Pakistan's chief army spokesman, Maj-Gen Athar Abbas, said the bomber had targeted a convoy leaving the base in Wana, where troops were protecting a deployment of Pakistan's Frontier Corps.
"I can confirm eight soldiers were killed," he told the BBC.
"The convoy was just leaving the fort when the attack happened. We believe the actual target was the fort itself."
The attack came two days after suspected US missile strikes in the region killed about 20 people.
Maj-Gen Abbas said he believed Sunday's bombing could have been a response by militants in the area.
Locals told the BBC that security forces had closed down the main road in the area following the attack, forcing traffic off the road.
South Waziristan, a tribal district in Pakistan's Federally Administered Tribal Areas (Fata), was the first significant sanctuary Islamist militants carved for themselves outside Afghanistan after the US-led invasion of that country in 2001.
In recent times, Azam Warsak has been the scene of many such attacks on the Pakistani soldiers, the BBC's Syed Shoaib Hasan reports from Islamabad.
On 22 June 2002, it was the scene of the first operation against al-Qaeda by the Pakistan army. The army lost 11 soldiers on that day, which marked the beginning of conflict between the army, al-Qaeda and the Taleban.
The area is currently controlled by Taleban commander Mullah Nazir, who is believed to be behind many cross-border attacks against coalition forces in Afghanistan.
Mullah Nazir rose to prominence in March 2007, when he chased Uzbek militants from the Islamic Movement of Uzbekistan (IMU) out of South Waziristan, our correspondent says.
He was on good terms with the Pakistani army until the recent missile strikes began in Waziristan.
Local residents say Friday's attack has heightened tensions, and could cause major problems for the army in Waziristan.
This could complicate matters, as security forces are still caught up in a massive operation in the nearby tribal region of Bajaur.