The building of the barbed wire anti-insurgent fence however provoked anger from Kabul, which says it does not recognise the porous frontier between the two pivotal allies in the US-led "war on terror".

"We have completed 20 kilometres (12 miles) of fencing in North Waziristan's Lwara Mundi area," spokesman Major General Waheed Arshad told AFP in an interview at his office in the garrison city of Rawalpindi.

"This is that difficult part where most militants reportedly were crossing over."

Another 15-kilometre stretch would soon be fenced in the neighbouring South Waziristan tribal area, Arshad said. The army has also deployed extra troops and increased patrols in the area, which faces southeastern Afghanistan.

Lwara Mundi is tiny and remote settlement located in a gap between two mountain ranges through which Arshad said militants were driving vehicles and heavy weapons.

North and South Waziristan and other Pakistani tribal areas along the rugged border have been branded by US and Nato officials as havens for Taliban and al-Qaeda insurgents launching attacks into Afghanistan.

Pakistani President Pervez Musharraf formally announced plans in February to build a fence along parts of the frontier. He said plans to mine it had been postponed after international criticism.

More than 1,000 people have died in Taliban-related violence in Afghanistan this year including around 50 foreign soldiers. The majority of the bloodshed has been in provinces bordering Pakistan.

But Kabul does not recognise the international border first drawn up by colonial Britain in 1893 and wrote to United Nations chief Ban Ki-moon earlier this year to express "deep concern" over the fencing plans.

Afghan foreign ministry spokesman Sultan Ahmad Baheen said Thursday that "the Afghan government is against fencing the border. It separates families and people living on both sides."