ISLAMABAD, Dec. 23 (Xinhua) -- Four troops were killed and 15 others injured during a clash between security forces and terrorists in Pakistan's northwest Khyber Pakhtunkhwa province, official sources said.

The incident happened on Sunday in the rugged Tirah Valley area of Khyber tribal district of the province, where security forces conducted a search operation, and intermittent exchanges of fire were reported throughout the day, the sources told Xinhua on anonymity.

Immediate medical assistance was provided to the injured people at the site before they were sent to a nearby military hospital, the sources added.

The Pakistani military has yet to issue an official statement regarding the incident.

The Tirah Valley, situated along the Pakistan-Afghanistan border, has long been a focus of counterinsurgency efforts due to its strategic location and history of militancy. ■