Militants stormed a security checkpoint in Pakistan's northwest near the Afghan border, killing six soldiers, three police and security sources said on Tuesday.

The attack in the former tribal district of Kurram comes as Pakistan and Afghanistan struggle to maintain a fragile truce after border clashes killed dozens in October, their worst fighting since the Taliban took control of Kabul in 2021.

Islamabad has blamed a surge in violence in Pakistan on militants who use Afghan soil to plan their attacks on security forces across the border. Kabul has denied the charges, saying Pakistan's security is an internal problem.

No group has claimed responsibility for the attack, which the sources said took place between Monday night and Tuesday morning.

Kabul and Islamabad, once longtime allies, have engaged in intermittent border skirmishes since October, including heavy firing on Friday that killed at least five people.

Three rounds of peace talks hosted by Qatar, Turkey and Saudi Arabia have failed to produce a lasting agreement.

Their mountainous border regions are home to Islamist militants from the Tehreek-e-Taliban (TTP), also known as the Pakistani Taliban, who have waged a war against the state for nearly 20 years.

The TTP adheres to a strict interpretation of Islamic law akin to their counterparts in Kabul, although the Afghan Taliban maintains that they do not share an operational relationship with the group.