At least two Frontier Corps (FC) personnel deployed on the Pak-Afghan border were martyred, while five were injured in an attack from across the border, the Inter-Services Public Relations (ISPR) said on Sunday.

The attack was carried out from the Khost province of Afghanistan on a border post in Laka Tika area of Lower Kurram Agency, officials of the political administration in Kurram Agency said.

ISPR, the Army's media wing, said FC troops were fired upon from Afghanistan while they were busy in "routine surveillance along Pak-Afghan border for plugging of gaps and making necessary preparations for starting fencing in that area."

"Pakistani troops are exercising maximum restraint so as to avoid any Afghan civilian casualties," the statement said, adding: "Military engagement is underway to defuse [the] situation."

According to government officials, scores of armed tribesmen from Bangash and other tribes have started assembling to support the security personnel.

Tribal elders reportedly made announcements at several mosques in the nearby areas, appealing tribesmen to join the security personnel on the border. Following the announcements, several armed tribesmen, belonging to Toori Bangish and other tribes started approaching the border posts.

An investigation into the firing incident has been initiated.

Kurram is one of the most sensitive tribal areas as it borders three Afghan provinces and at one point was one of the key routes for militant movement across the border.

Pakistan began fencing the Pak-Afghan border last year to prevent terrorists from crossing into the country from Afghanistan.

The two countries accuse the other of harbouring their militant enemies — both deny the other's charges.