By Ibrahim Shinwari
BARA, Pakistan, March 2 (Reuters) - Militants attacked a hilltop army position in volatile northwest Pakistan on Friday in a clash in which at least 33 people were killed, a security official said, the latest skirmish in a campaign in which neither side appears to have the upper hand.
At least 10 Pakistani soldiers and 23 militants were killed in the clash in the remote Tirah Valley in the Bara area of Khyber, near the Afghanistan border.
"Dozens of militants attacked three recently established security checkpoints. That led to heavy fighting," a military official told Reuters, requesting anonymity because he is not authorised to speak to the media.
Casualties could not be independently verified, and militants often dispute official accounts.
Several Pakistani military offensives in the tribal regions such as Khyber have failed to crush militant groups.
The insurgency is led by the Pakistani Taliban, formally known as the Tehrik-e-Taliban Pakistan, which has an active faction in Khyber.
The military campaign along the entire border region and across several tribal agencies involves more than 100,000 Pakistani troops, but it has effectively reached a stalemate in many areas.
Formed in 2007, the TTP is an umbrella organisation of militant groups allied with the Afghan Taliban and al Qaeda. It pledged to overthrow the Pakistani government after the military stepped up operations against militants five years ago.
Khyber is one of seven ethnic Pashtun tribal regions along the porous border which have never come under the full control of the state. Militants have taken advantage of the area's lawlessness to set up strongholds.
Khyber is one of the main land supply routes to Afghanistan for U.S.-led NATO troops, suspended by Pakistan after a cross-border clash in November last year that left 24 Pakistani soldiers dead. (Additional reporting by Jibran Ahmad in PESHAWAR and Saud Mehsud in DERA ISMAIL KHAN; Writing by Qasim Nauman; Editing by Chris Allbritton and Nick Macfie)