PESHAWAR, Pakistan — At least 19 people were killed in an explosion on a bus traveling in the North Waziristan tribal region on Sunday.

There were conflicting reports about what may have caused the blast, with some government officials saying it was a terrorist act while others insisting the explosion was caused by a gas cylinder.

The bus was taking passengers from Bannu district of the Khyber Pakhtunkhwa province to Mir Ali subdivision in the volatile North Waziristan tribal region.

Two government officials in Mir Ali subdivision said a suicide bomber was traveling in the bus from Bannu to Mir Ali and it seemed he mistakenly triggered his explosives-laden jacket and caused the blast.

Government officials said the passenger coach was completely destroyed by the blast.

A government official said none of the passengers survived.

"Only pieces of their bodies were collected from spot of the blast and were beyond recognition," the official said.

The official said there was a gas cylinder installed in the vehicle but that it wouldn't cause a lot of destruction if it were to explode.

A security official said investigators were trying to determine the nature of the blast, but said it seemed to be a terrorist act.

PESHAWAR, Pakistan – An improvised explosive device detonated amid a Pakistani military convoy deployed to fight al-Qaida and militant groups Sunday in the volatile North Waziristan tribal region, leaving 16 army soldiers dead and 22 wounded, military officials said.

The attack took place only a day after Pakistani Taliban leader Hakimullah Mahsud asked his fighters to refrain from attacking Pakistani security forces and government installations in North Waziristan and abide by a peace accord signed between the government and regional Taliban led by Hafiz Gul Bahadur.

No militant group claimed responsibility for the deadliest attack on Pakistani security forces, though military authorities and government officials blamed anti-Pakistan militant organizations opposed to the restoration of peace in North Waziristan.

Military officials said the local administration had banned civilian traffic from roads in all of North Waziristan on Sunday because of the movements of the security forces in the tribal region.

The officials said unknown people planted the IED on the Miranshah-Razmak road which went off when the military convoy passed through the mountainous Narray Wala area.

Government officials in the Razmak subdivision said two heavy military trucks were damaged in the blast. They said one of the trucks, which was carrying more than two dozen soldiers, plunged into a 1,000-foot-deep ravine after being hit by the IED.

They said they believe most of the soldiers died when the truck fell into the ravine.

Military officials said it took hours of frantic effort to recover the bodies and injured soldiers from the ravine before dark. Most of the injured were airlifted to military hospitals in Bannu and Peshawar.

Military sources said they feared the death toll would rise because most of the injured were in critical condition.

An official of the Inter-Services Public Relations (ISPR) had the death toll at 14 soldiers and the number of wounded at 22. The discrepancy in the death toll was not explained.

Government and military authorities said the attack came as a surprise after Mahsud asked his fighters to abide by the peace accord signed between the government and local Taliban in North Waziristan.

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Government officials speculated that there might be elements within the Pakistani Taliban who did not want peace to prevail in North Waziristan or there could be a foreign presence trying to create mistrust between the tribespeople and armed forces.

One of the officials in Miranshah said that military officials were encouraged enough by the peace initiative by the Taliban militants that they relaxed curfew for the local tribespeople three times on Sunday on the road where the attack took place so expectant mothers could be taken to hospital to give birth.

"Nobody expected an attack on Pakistani forces," a government official said on condition of anonymity.

The militants affiliated with Mahsud on Saturday issued a pamphlet in which the leader directed his men to abide by the peace agreement between local Taliban and the government for the maintenance of law and order in North Waziristan.

Pakistani Taliban spokesman Ihsanullah Ihsan, calling from an undisclosed location, confirmed the Mahsud directive.

"Oh, mujahedeen brothers! As you know that the Pakistani and Afghan Taliban under the leadership of Mullah Mohammad Omar Mujahid are engaged in jihad against the crusaders and infidels, and are supporters of each other in the ongoing holy war, the enemies do not want to see us united and disciplined against them and are being trying to divide us," Mahsud said in the pamphlet.