Secretary of State Rex Tillerson said in Afghanistan Monday that he believes a "moderate voice among the Taliban" could hold the key to ending the war in Afghanistan.

"They don't want their children to fight forever," Tillerson said of members of the Taliban during a surprise visit to the country Monday. "So we are looking to engage with those voices and have them engage in a reconciliation process leading to a peace process and their full involvement and participation in the government."

Tillerson made the remarks during a surprise visit to Bagram Airfield, as he travels through the Middle East on diplomatic missions intended to counter Iran's growing influence in the region. Tillerson is also seeking to implement a new strategy for the war that encompasses the relationship with neighboring Pakistan, as the United States tries to stifle support for an insurgency against the Afghan government.

"If you consider the current situation in Afghanistan – and we were talking about this a few minutes ago – and you look a few years in the past and what the circumstances were, Afghanistan has come quite a distance already in terms of creating a much more vibrant population, a much more vibrant government, educational systems, a larger economy," Tillerson said. "And so there are opportunities to strengthen the foundations for a prosperous – a prosperous Afghanistan society."

The trip coincides with a renewed focus on American military commitments following the death of four troops in Niger. That raised questions of whether the conflict is a "forever war," as the Taliban carries out new attacks. The insurgents have started using Humvees captured from Afghan forces for suicide bombings, and they over-ran an Afghan military base last week that was garrisoned by 60 soldiers. But dozens of Taliban fighters were also killed in clashes between two rival militant groups.

"Clearly, we have to continue the fight against the Taliban and against others in order for them to understand they will never win a military victory," Tillerson said. "And there are, we believe, moderate voices among the Taliban, voices that do not want to continue to fight forever."