In the rugged mountains of Pakistan, the resurgent Pakistani Taliban are waging a relentless and deadly guerrilla war against Pakistani security forces, in the biggest terrorism threat the South Asian nation has faced in a dozen years.

Pakistan has responded to the insurgency, which was nearly defunct just four years ago, with drone strikes and what it has called targeted operations. But in the process, the military has lost hundreds of armed personnel, displaced tens of thousands of people and stoked anger among local communities.

Pakistan’s shaky grip on its mountainous western regions, along the border of Afghanistan, is compounded by the presence of Islamic State fighters in the same areas. The increasing militant activity has threatened Pakistan’s positioning as a military powerhouse in South Asia, a status that it has been taking measures to consolidate this year.

Pakistan’s powerful army chief, Gen. Syed Asim Munir, met President Trump at the White House last month — their second meeting in just over three months. The Pakistani military downed Indian jets with Chinese technology earlier this year. And Pakistan’s government signed a defense pact with Saudi Arabia last month.

Yet the Pakistani Taliban have presented Pakistan with its fiercest security challenge in years, security analysts say.