Pakistani forces attacked militants in mountains near the Afghan border on Monday as fresh troops arrived after heavy fighting with Taliban insurgents, government officials said.

More than 600 al Qaeda-linked militants attacked a paramilitary force camp and two checkposts in the Mohmand region, to the north of the city of Peshawar, Saturday night killing six soldiers and wounding seven, the force said.

Security forces pushed back the militants, who had attacked from the direction of the Afghan border, killing 40 of them in hours of fighting, the paramilitary force said. There was no independent verification of the toll.

Pakistani forces fired artillery at militant hideouts in mountains above two villages Monday, said a senior government official in Mohmand, Meraj Khan.

“Heavy firing is going on in the mountains but we don’t have any details of casualties yet,” Khan told Reuters.

Mohmand is to the south of the Bajaur region, also on the Afghan border, where Pakistani forces have been involved in heavy fighting with militants since August.

The military has said more than 1,500 militants have been killed in Bajaur but there has been no independent verification of that estimate.

The campaign in Bajaur has been coordinated with U.S. forces across the border, in Afghanistan’s Kunar province, in an effort to squeeze the militants out. Some of the militants in Mohmand are suspected to have come from Bajaur, Khan said.

Another official in Mohmand, Syed Ahmed Khan, said extra soldiers and equipment, including tanks and armoured personnel carriers, arrived at a military camp in Ghalanai, the region’s main town, Monday.

The United States and Afghanistan have for years been urging Pakistan to do more to tackle militants operating out of lawless enclaves on the Afghan border which no government has ever controlled.

Pakistan has had about 100,000 troops on its western border with Afghanistan although it recently withdrew “limited numbers” because of tension with India after a militant assault on the Indian city of Mumbai in November.

Pakistani troops pound militants in northwest mountains – International Herald Tribune