ISLAMABAD, June 3 (Xinhua) -- At least six militants were killed and several others injured as Pakistani forces retaliated cross-border attacks by militants from the Afghan side on Sunday, the Pakistani army said in a statement here.

The Inter-Services Public Relations (ISPR), the media wing of Pakistan army, said that the militants attacked Pakistani security personnel who were busy in border fencing in the country' southwest Balochistan and northwest Khyber Pakhtunkhwa provinces.

"Taking advantage of ungoverned spaces and facilitation inside Afghanistan, terrorists resorting to such attacks to prevent fencing and construction of border posts," said the statement.

Five soldiers including four from paramilitary troops Frontier Corps and one from Pakistan air force sustained injuries in the attack, the statement added.

Identities of the killed militants were not revealed.

Pakistan is investing heavily to construct a chain-link fence at its over 2,000-km-long border with Afghanistan, in Balochistan and Khyber Pakhtunkhwa provinces to restrict the penetration of militants into Pakistani territory from Afghanistan.

The ISPR said that to consolidate the gains of successful kinetic operations against terrorism by the country's military, fencing of Pakistan-Afghanistan border and construction of border forts will continue irrespective of the challenges posed by inimical forces.