Five Pakistani soldiers were killed when terrorists from inside Afghanistan across the international border opened fire on the troops in Pakistan's northwest Khyber Pakhtunkhwa province, a military statement said on Sunday.

The incident happened at the border area in Kurram district of the province, the military's media wing Inter-Services Public Relations said in the statement.

The Pakistani troops retaliated the attack "in a befitting manner", and as per intelligence reports, the terrorists have suffered heavy losses, said the statement.

"Pakistan strongly condemns the use of Afghan soil by terrorists for activities against Pakistan," it added.

The Pakistani army is determined to defend the country's borders against the menace of terrorism, the statement said.