ISLAMABAD - Pakistan said Saturday four of its soldiers were killed and another was injured when "terrorists" from across the Afghanistan border opened fire at two locations.

The deadliest of the shootings occurred in the remote Dir district where Pakistani troops were building a border fence when they came under attack from the other side, killing three soldiers and injuring another.

The military's media wing said another soldier was killed when "miscreants" from the Afghan side ambushed a routine border patrol party late Friday in North Waziristan district. It added that two of the assailants were also killed in an exchange of fire.

Cross-border militant attacks are not uncommon on Pakistani troops constructing a fence along the country's nearly 2,600 kilometer border with Afghanistan.

Islamabad began the unilateral fencing of the largely porous frontier two years ago to plug hundreds of informal crossings that were encouraging terrorist infiltration in both directions.

Military officials expect the massive border project will be in place by end of next year, addressing to a large extent mutual concerns of illegal crossings of both militants and drug traffickers.

Pakistan has complained that anti-state militants linked to the Tehrik-e-Taliban Pakistan, or TTP, have taken refuge in "ungoverned" Afghan border areas after fleeing Pakistani security operations and orchestrate attacks from those sanctuaries.

Earlier this week, the United States designated TTP chief Qari Wali Noor Mehsud a global terrorist for directing deadly attacks against Pakistan.

Mehsud's whereabouts are not known but his predecessor, Mullah Fazlullah, was killed in June of 2018 along with several key TTP commanders in an American drone strike in an eastern border region of Afghanistan.

For their part, officials in Kabul allege that leaders and fighters of the Afghan Taliban use sanctuaries on Pakistani soil to direct insurgent attacks against local and international forces.