The US-led military campaign in Afghanistan is shifting its focus from Taliban strongholds in the south to the Pakistani border, where troops will likely fight until 2014.
With NATO forces on deadline to end their combat mission within three years, coalition leaders believe major offensives against Taliban rebels in the southern provinces of Kandahar and Helmand have turned the tide in the war.
The east is now the new priority, as strategists work out how to contain Islamist militant groups such as the Taliban, Al-Qaeda and the Al-Qaeda-linked Haqqani network, embedded in the border areas with rear bases in Pakistan.
The United States may be withdrawing 33,000 soldiers by the end of next summer, but it is boosting troops in the eastern province of Khost, where officers talk of taking the fight to the enemy and winning the decade-long war.
"Most nights of the week, US special forces are in action here taking out enemy operatives," said Aaron Tapalman, the 28-year-old army captain in charge at Combat Outpost Sabari.
"We are aggressive, we are getting out there to challenge the insurgents and push ahead to provide security.
"This area has been a safe haven for several years and we are determined to make progress and change things."
Tapalman's post takes regular mortar fire, a surveillance balloon scans the ground for rebel attacks and foot patrols thread their way through fields laced with bombs.
"Some areas of Afghanistan are transitioning (to Afghan control) but districts like Sabari are well behind that," he said, pointing out that only five of the 53 district administration positions are currently filled.
In the absence of government structures and security, the Khost provincial reconstruction team (PRT) encourages warring local tribes to unite against the insurgents who transit through Khost carrying weapons and explosives.
"This is not the right environment for reconstruction projects," said Sabari PRT leader Captain Steve Baunach.
"The kinetic battle is pushing insurgents out of Afghanistan, and they are moving east to key exit points. Khost has been a traditional embarkation point for insurgents from Pakistan, so the fight here will pick up."
The challenge of extending the government's reach to eastern border areas is even more acute in the mountainous provinces of Nuristan and Kunar.
American anthropologist Richard Strand, an expert on Nuristan, told AFP that the Taliban had effectively taken control of Kamdesh district after the United States withdrew from remote border posts in 2009 and 2010.
"Taliban thugs are beating people up, murdering teachers and closing down schools. They even have their own jail," said Strand, one of the few Westerners in regular telephone contact with residents of the region.
"This is a huge morale boost for the Taliban. The loss of much of Nuristan bodes ill for the rest of the Afghanistan. The US didn't have the resources and the Taliban exploited that."
Outgoing US commander General David Petraeus on July 4 confirmed more "intelligence, surveillance and recognisance assets" would be moved east, while troops have also been back in the rugged mountains to thwart insurgent advances.
Critics of the speed and size of the US drawdown have warned that it may not leave enough troops to achieve maximum success in the east.
But for others, the real problem is rear bases in Pakistan's semi-autonomous tribal belt just across the border. There, the US fight is confined to drone strikes, as Islamabad has refused to countenance US boots on the ground.
As President Barack Obama reduces troop numbers, his commanders must strike a compromise between consolidating gains in the south and concentrating on the east, where some of the fiercest insurgent groups are active.
"It is fair to say that senior officers from the two theatres are competing over troops," said one US officer. "It is a matter on which a lot hangs."
The debate highlights a long-standing question over US goals in Afghanistan, said Seth Jones of the Washington-based Rand Corporation think-tank.
"If it is about counter-insurgency, then the south should be the focus. But if it is about counter-terrorism, then the east should be," he said.
The May killing of Osama bin Laden in Pakistan completed a key US war goal, and was seen as a boost for those in Washington such as Vice President Joe Biden who back a smaller-footprint, counter-terrorist approach.
Jones said the new emphasis on the east was a return to the region's basic power balance. "It is where you find Al-Qaeda and other militant groups associated with them," he said.