Republican White House hopeful Mitt Romney on Tuesday said the US military should not "cut and run" in Afghanistan, as such a move could jeopardize the massive US investment in the region.

Romney, battling to stay ahead in the race for the Republican presidential nomination in the face of a surging Newt Gingrich, said a sizeable US force needed to remain for intelligence gathering and special forces operations.

"We can't just say good-bye to all of what's going on in that part of the world. Instead we want to draw them towards modernity," Romney said at a Republican debate on national security.

He said pulling out troops faster than planned would "put at great peril the extraordinary sacrifices that have been made."

"This is not time for America to cut and run," said Romney, the former governor of Massachusetts.

Jon Huntsman offered a strong rebuttal, saying the United States had achieved "some very important goals" in Afghanistan but should now drastically reduce its involvement from the present almost 100,000-strong force.

"We need a presence on the ground that is more akin to 10 to 15,000 that will help with intelligence gathering and special forces responsibility," the former Utah governor said.

"We need an honest conversation about the sacrifices that have been made over nearly 10 years," Huntsman said.

"We have dismantled the Taliban, we've run them out of Kabul. We've had free elections in 2004, we killed Osama bin Laden, we upended, dismantled Al-Qaeda."

Afghanistan and the United States are currently negotiating a strategic partnership that will govern bilateral relations after NATO combat forces -- there are currently 140,000 in the war-torn state -- withdraw in 2014.

The United States has increasingly been looking for a negotiated end to the Afghan conflict given that the insurgency remains virulent more than 10 years after the September 11 attacks prompted American forces to invade the country.

A US troop surge was credited for improving security in the troubled south but Pentagon officials have said President Barack Obama's administration is contemplating scaling back Afghan combat operations much earlier than planned.