ISLAMABAD, May 13: Pakistani and Afghan forces exchanged fire at their rugged border on Sunday in their most serious skirmish in years. Pakistan said it killed five Afghan soldiers, but Afghanistan said just two Afghan civilians died.

Tension has been running high between Afghanistan and Pakistan over controlling the 2,430-kilometre border and stemming the flow of Taliban and Al Qaeda terrorists that stage cross-border attacks inside Afghanistan. Pakistan's move to fence parts of the disputed frontier has also angered Afghanistan.

Pakistan army spokesman Maj-Gen Waheed Arshad accused the Afghan army of sparking the two-hour gunbattle with “unprovoked” fire at about six Pakistani border posts in Kurram Agency, a tribal region opposite Afghanistan's Paktia province.

A Pakistan military statement said troops from its Frontier Corps returned fire and five Afghan National Army soldiers were killed. Arshad initially put the toll at six or seven and said three Pakistani troops were wounded.

“This was unprovoked and without any reason,” Arshad said.

On the Afghan side, Defence Ministry spokesman Gen. Mohammad Zahir Azimi accused Pakistani forces of encroaching 2 to 3 kilometres inside Paktia province's Jajai district.

“Border police tried to stop them, and the Pakistani army started firing heavy weapons toward the Afghan forces,” he told a news conference.

Two school students were killed, and three students and two police were wounded, he said. Earlier, the chief of Afghan border police, Gen. Abdul Rahman, said five police were wounded.

Paktia Governor Rahmatullah Rahmat said heavy weapons fire hit the village of Kubki and a school, bazaar and clinic in Gul Ghundi village, wounding villagers and students.

“The Pakistanis launched artillery, shot their guns, and they left behind civilian casualties in the area. It is a clear violation -- crossing the border to attack Afghanistan,” Rahmat said. He said Afghan forces only fired back with assault rifles.

Azimi claimed that thousands of local people had gone to join the Afghan forces after the clash, which he described as the worst in years between the two countries.

The Pakistani side later denied its forces had entered Afghan territory or that they had hit civilian targets.

Frontier Corps commanders had complained to Nato in Afghanistan about Afghan attempts to occupy trenches in Kurram's Gavi area, the military statement said. It also accused Afghan troops of firing on a helicopter carrying Nato officials to Gavi to meet Afghan and Pakistani officials, forcing it to return to base.

Nato officials in Kabul could not be reached for comment.

The incident was likely to enflame the already acrimonious relations between the two key US allies -- just two weeks after a reconciliation meeting between President Gen Pervez Musharraf and Afghan President Hamid Karzai in Turkey where they agreed to jointly fight terrorism.—AP