At least 15 militants and four soldiers were killed during clashes in a tribal district in northwest Pakistan, security officials said Saturday.

The confrontation started on Friday and continued until Saturday morning in Khyber, one of the seven tribal districts along the Afghan border, officials said.

"During exchange of fire, troops killed at least 15 militants and destroyed their two hideouts," a senior security official told AFP. "Four soldiers also embraced shahadat (martyrdom) in the operation," the official added.

Another security official also confirmed the toll, which could not be verified by independent sources.

It was not clear how the clashes began, but Pakistan troops have been targeting Taliban and Lashkar-e-Islam militia in a recent military push in the important Khyber tribal district.

The key area straddles the NATO supply line into Afghanistan, used by US-led troops to evacuate military equipment ahead of their 2014 withdrawal.

Pakistani troops have been fighting for years against homegrown insurgents in the tribal belt, which Washington considers the main hub of Taliban and Al-Qaeda militants plotting attacks on the West and in Afghanistan.