At least 25 militants were killed and 23 others injured in the latest military operation in northwest Pakistan's Orakzai tribal agency on Thursday, army sources said.

During the clashes with militants in Lower Orakzai area, one soldier was killed and three others injured, the army said.

Three militants were arrested during the search and clearance operation.

Official sources said that five militants were killed in a clash with security forces in Sangara area of Orakzai earlier the day.

Unknown militants destroyed a local Basic Health Unit (BHU) in Akhonkot area of Upper Orakzai agency by putting explosive material in the building.

More than 399 militants have been killed so far since the operation started in late March in the area, that has seen a growing number of Taliban and al-Qaeda militants who fled South Waziristan tribal area due to the military operation.

Moreover, security forces killed four militants Thursday in a clash in Swat valley, northwest of Pakistan, and shelled militant' s hideouts in Bara tehsil of Khyber tribal region.