The campaign, involving 3, 000 Pakistani soldiers, took back much of Mohmand from the Taliban.

WSJ: Airstrike Ravages U.S.-Pakistan Ties

Mohmand is one of seven semi-autonomous tribal agencies along the 1, 500-mile border that Pakistan shares with Afghanistan.

CNN: STORY HIGHLIGHTS

But Pakistan's army says Taliban militants continue to mount attacks on its forces in Mohmand from across the border in Afghanistan.

WSJ: Airstrike Ravages U.S.-Pakistan Ties

Umar was arrested in Pakistan's Mohmand Agency, one of seven semiautonomous tribal agencies along the 1, 500-mile porous border that Pakistan shares with Afghanistan, intelligence officials said.

CNN: Two Pakistani Taliban leaders captured

Pakistan says it has increased the number of soldiers at border posts like these as part of a campaign in Mohmand this year to wipe out the Taliban in the area.

WSJ: Airstrike Ravages U.S.-Pakistan Ties

In the 1990s, Samia Sarwar Mohmand, a young Pathan girl who wanted to marry of her own free will was shot dead in the office of Pakistan's most relentless women's rights campaigner Asma Jehangir.

BBC: NEWS | South Asia | Ramifications of a gang rape

Now it's fighting in Mohmand, closer to Peshawar.

BBC: Pakistan's spreading Taleban war

As U.S. military, Pakistani forces and Afghan officials sought to piece together the incident, Afghan, U.S. and Western officials said the attack took place in response to fire from the remote Pakistani posts in the Mohmand tribal region, a lawless border area that abuts Afghanistan's eastern Kunar province.

WSJ: Airstrike Ravages U.S.-Pakistan Ties