RAWALPINDI, PAKISTAN - PAKISTAN'S military said on Tuesday 42 militants were killed during some of the heaviest fighting reported from the frontlines of its offensive against the Taleban in their tribal sanctuaries.

The latest death toll brings to 239 the total number of insurgents killed during the operation, but no information provided by the army can be verified with communication lines down and access banned to journalists and aid workers.

An army statement said troops fought at multiple locations in the far north of South Waziristan, where ground forces thrust towards die hard Taleban positions from their rear base at Razmak, killing 30 militants.

Security forces have surrounded Nawazkot, one of the Taleban's main regional strongholds and another 12 militants were killed in fighting on the approach to Taleban bastion Sararogha to the east and Kanigurram further south.

The death of a soldier brought to 31 the total number of troops reported killed since the operation began 11 days ago.

Around 30,000 troops are taking part in the offensive against an estimated 10-12,000 militants in the semi-autonomous and lawless tribal belt.

Relief workers say that around 200,000 people have been displaced by the fighting.