A bomb ripped through a vehicle carrying security forces inside a Pakistani army compound in the country's volatile northwestern region Sunday, killing at least 18 people, most of them paramilitary troops, security officials said.

The vehicle was hired by the paramilitary Frontier Corps, said police official Inyat Ali Khan from the Bannu region where the explosion occurred. It was part of a convoy that was about to leave the military base in the town of Bannu and drive south to the North Waziristan tribal area, he said.

Troop rotation

The convoy was part of a regular Sunday morning troop rotation going into North Waziristan, said a military source who did not want to be identified because he was not authorized to speak to the media. He said the bulk of the casualties were from the Frontier Corps because the bomb was planted in a vehicle hired by the paramilitary force to transport their personnel but he could not confirm whether any civilians were killed.

Khan put the dead toll at 18 while the military official said 20 were confirmed dead and another 30 were wounded, many of them critically. Such conflicting death tolls are common in the chaotic aftermath of bombings, especially when victims are often taken to different hospitals. 

Often hit by bombs

North Waziristan is considered a safe haven for al-Qaida linked militants. Pakistani troop convoys often are hit by roadside bombs, but blasts inside a compound are rare.

The Pakistani military has been fighting for years against militants in the tribal areas who want to overthrow the government and establish a hardline Islamic state across Pakistan. The militants view the army and other military forces as carrying out an American agenda in the tribal areas, which border Afghanistan and are also seen as a refuge for insurgents in that country.