Pakistan on Thursday protested the killing by Afghan soldiers of 14 people Pakistan claims were its citizens, the latest source of tension between the neighboring countries amid increasing violence along their rugged border.

Pakistan's Foreign Ministry summoned the Afghan ambassador to lodge the protest and "demanded an independent investigation into the incident and punishment for those responsible," said Foreign Ministry spokeswoman Tasnim Aslam.

At least 14 bullet-riddled bodies were found Tuesday in southern Afghanistan and returned to the Pakistan border town of Chaman on Thursday.

Afghan authorities have opened an investigation amid conflicting claims the victims were Taliban fighters from Pakistan or Pakistani tribesmen traveling to a religious festival in northern Afghanistan.

The Afghan Embassy in Islamabad was closed for a public holiday Thursday, and officials there could not be reached for comment.

Afghanistan and Pakistan have differed over claims that Taliban fighters and leaders find sanctuary inside Pakistan. Afghanistan has long demanded that its neighbor do more to crack down on militant Taliban supporters, while Pakistan says it does all it can to patrol the 1,470-mile frontier with 80,000 forces.

Insecurity has surged along the border, a concern for the United States four years after the American-led invasion to oust Afghanistan's Taliban regime for harboring Osama bin Laden.

A local Afghan army commander, Abdul Razzak, claimed the victims were Taliban fighters and that his soldiers killed them during a two-hour battle near Spin Boldak, an Afghan town opposite Chaman.

Razzak said one of the victims was a midlevel Taliban commander, Mullah Shien, who for months has allegedly led several cross-border raids from secret bases on the Pakistani side of the frontier.

But Saqib Aziz, a Pakistani government official in Chaman, claimed the victims were Pakistanis from the Noorzai tribe who were killed over a feud with Razzak's clan. The victims will be buried in the nearby Pakistani village of Boghra.

Aziz said the men had been planning to travel to the northern Afghan city of Mazar-e-Sharif to celebrate Nowruz, an ancient Persian spring festival that also marks the new year in Afghanistan.

The governor of Afghanistan's southern Kandahar province, Haji Asadullah Khalid, opened an investigation Wednesday and said initial information indicated they were Afghan refugees who had been living in Chaman and involved in cross-border criminal activities.

In Pakistan's South Wazirirstan tribal region, meanwhile, suspected Islamic militants opened fire Thursday on a car carrying an Islamic cleric, killing him and abducting his three body guards, an intelligence official said on condition of anonymity because of the secretive nature of his job. One of the guards later escaped.

Cleric Maulvi Sibghatullah's killing in the small town of Ladha on Wednesday appeared to be a result of internal differences among Islamic militants because he was believed to be trying to set up a breakaway faction, the official said.