PESHAWAR, Feb 28: Eleven people were killed and six wounded on Saturday when troops opened fire on passenger pickups in the South Waziristan tribal region mistaking them for militants, sources told Dawn.

They said the incident, which took place at around 8am near Wana, followed a late night mortar attack by suspected militants on an army brigade camp at Zeray Noor. The attack began at 3am and a total of 15 mortars were fired at the camp intermittently. An army hawaldar, Khizar Hayat, was wounded in the attack, the sources added.

Suspected militants also fired mortars on the Wana camp that houses offices of the agency's political agent, the sources said.

Officials said a team of army engineers was dispatched to defuse unexploded mortars near Shulam checkpost in the morning. At around 8am, a white colour double-cabin Datsun pickup with four people, believed to be militants, fired Kalashnikov shots in the air after watching the army engineers defusing the mortars, the sources said.

The army engineers immediately radioed the checkpost guards, asking them to intercept the vehicle.

The sources said army troops fired at the vehicle when it tried to speed through the checkpost but while the suspected militants managed to pass through safely a passenger vehicle coming behind was caught in the fire. Seven passengers of the second pickup were killed on the spot, while six others, including two boys, were wounded.

Four passengers travelling in another pickup coming from the opposite direction were also killed in the shooting. It was not immediately clear why the soldiers manning the checkpost fired at the other vehicle.

Witnesses said all the passengers were unarmed civilians. Sixof the 11 dead were Afghan refugees living in Wana, official sources said.

Tribal elders told Dawn by phone from Wana, the agency's headquarters, that the incident had caused a strong resentment among the local people.

An ISPR spokesperson, however, said that two to three vehicles came towards a Frontier Corps checkpost and fired at the militia manning it.

"The FC retaliated and in the cross-fire there have been a few civilian casualties who may possibly be terrorists," the spokesperson said.

"The chances of some civilians having been killed cannot be ruled out," he said.

Sixteen people had been arrested and the political authorities had launched an investigation into the incident, the ISPR said in a statement issued from Islamabad.

Officials in Peshawar, however, denied that any inquiry had been ordered. "Political authorities have nothing to do with the incident," said an official.

The authorities in South Waziristan, the largest of the seven tribal regions bordering Afghanistan, have imposed an immediate ban on carrying of weapons in Wana to pre-empt any trouble.

Agency's administrator Azam Khan said he had convened a jirga of tribal elders on Sunday where he would announce cash compensation for the victims.