MOHMAND AGENCY: Militants armed with heavy weapons attacked a checkpost in the Pak-Afghan border area of Salala killing four security personnel on Monday, DawnNews reported.

Retaliatory firing by the security personnel at the checkpost killed 20 militants.

No government official was available to verify the incident.

The border checkpost situated at Salala gained international exposure after a US military helicopter attacked a military checkpost of the Pakistan military killing 24 soldiers in November last year.

The attack further strained the rollercoaster relations between the two countries and as a result Pakistan had blocked the route of Nato supplies demanding an apology.