US President Barack Obama said the US must have an "exit strategy" in Afghanistan even as it expands its military, diplomatic and economic fight against a Taliban insurgency.
"What we're looking for is a comprehensive strategy," Mr Obama said in an interview aired on CBS television's 60 Minutes show.
"There's got to be an exit strategy," he said. "There's got to be a sense that this is not a perpetual drift."
Mr Obama's comments come as he prepares to roll out a new strategy for Afghanistan, against a backdrop of rising insurgent violence that has questioned the viability of a seven-year-old US-led effort to create a functioning democracy.
He said a decision last month to send 17,000 more US troops to Afghanistan - largely to head off a spike in violence before elections in August - was the most difficult he has had to make since taking office.
"You know I think it is the right thing to do. But it's a weighty decision because we actually had to make the decision prior to the completion of (the) strategic review that we were conducting," he said.
US commanders have said as many as 30,000 additional troops are needed to overcome a stalemate in parts of Afghanistan. But some analysts caution against a gradual Vietnam-like escalation in a country historically hostile to outsiders.
"We may need to bring a more regional diplomatic approach to bear. We may need to coordinate more effectively with our allies. But we can't lose sight of what our central mission is," said Mr Obama.
He said the mission was the same as when the US went into Afghanistan after the September 11, 2001 attacks, adding that projecting violence against US citizens "is something that we cannot tolerate".
The strategy is expected to rely on a major expansion of Afghanistan's own security forces, wooing "moderate" insurgents, stepping up civilian aid efforts and embarking on ambitious diplomacy across the region.
From agricultural experts to engineers, civilians will be expected to beef up local government and tribal leaders, as Western officials are wary of relying too heavily on a weak Kabul government plagued by corruption.
At the moment, the US commander in Afghanistan, General David McKiernan, describes the war as a "stalemate".
Even if all goes to plan inside Afghanistan, top officials say the key to the conflict lies across the border in Pakistan.
"As long as you've got safe havens in these border regions that the Pakistani government can't control or reach, in effective ways, we're going to continue to see vulnerability on the Afghan side of the border," said Mr Obama.