The red, brick fort sits on a small, barren plain surrounded by snow-streaked mountains, several hundred metres from the Afghan border.

Brigadier Rizwan Aktar, commander of the fort, points from its high walls to a fracture in a nearby line of hills -- the Chandi Gap, a notorious militant crossing point, he says.

But he told reporters on a weekend tour of border defences in Pakistan's North Waziristan tribal region he and his men were determined to stop infiltration into Afghanistan: "The people who want to create any nonsense, we are going to control them."

Pakistan is a major US ally in the war on terrorism but US officials appear increasingly frustrated about the help a resurgent Taliban in Afghanistan is getting from the Pakistani side of the border.

Taliban leaders are operating from Pakistan where training, financing and recruiting are also taking place, they say.

Pakistan says it can't completely seal the 2,500 km border but it is doing all it can to stop infiltration.

But Pakistan says infiltration is a minor factor behind the Taliban surge. Rather, it's a cocktail of Afghan factors including anger over civilian deaths in military attacks, corruption and the booming drug trade that's fuelling the Taliban war, it says.