Defense chief Leon Panetta told US troops Wednesday they were winning the 10-year war in Afghanistan, during a visit focused on handing security to Afghans as US troops withdraw.

Panetta is in Afghanistan to review the war effort with the United States, which is on track to recall 33,000 troops by the end of the next year and is shifting its focus to an advisory role in training Afghan security forces.

"We're moving in the right direction and we're winning this very tough conflict," he told troops at Forward Operating Base Sharana, 56 kilometres (35 miles) from the Pakistan border, in the eastern province of Paktika.

In October, the Pentagon said that Taliban attacks were down for the first time in five years but that insurgent sanctuaries in Pakistan were feeding violence on the border and threatening the war effort.

"Are there challenges out there? You're damn right, there are challenges. Are we gonna be able to take on those challenges? You're damn right we will," Panetta told the troops.

"Ultimately here in Afghanistan, we will be able to establish a country that is able to govern and secure itself, we will make sure that the Taliban will never be able to find safe haven here, that Al-Qaeda will never again be able to find safe havens here."

Panetta said it was important to make sure Pakistan could secure their side of the border and that US support would continue for Afghanistan after 2014.

"Its difficult, it's complex, but at the same time it's important to maintain a relationship with Pakistan," he said.

America's alliance with Pakistan is in crisis over NATO strikes that killed 24 Pakistani soldiers near the Afghan border on November 26.

Islamabad has shut the US supply line into landlocked Afghanistan and forced Americans to leave a base widely reported to have been a hub for CIA drones.

As the United States draws the curtain on its eight-year venture in Iraq, Washington is determined to bring an end to the Afghan war as soon as possible.

Panetta meets President Hamid Karzai later Wednesday and earlier met Defence Secretary Abdul Rahim Wardak to discuss the security transfers, taking place in conjunction with the planned exit of NATO combat troops by the end of 2014.

"We will not simply pick up and get out. We spilled too much blood here," he told the troops.

The United States is withdrawing 10,000 troops this year, leaving 91,000 on the ground into 2012. Another 23,000 are to leave by the end of September 2012.

That will mark the end of the "surge" ordered by President Barack Obama in late 2009 in a bid to reverse the Taliban insurgency, defeat Al-Qaeda and speed up an end to the war, and will leave 68,000 US forces on the ground.

The US commander in Afghanistan, General John Allen, gave no date but said military operations would shift to a more advisory role, envisaging the introduction of special "advisory forces" embedded with Afghan troops.

He also indicated there could be a thaw with Pakistan, following a telephone conversation with Pakistan army chief General Ashfaq Kayani.

Allen said they discussed restoring coordination along the border in the hope that the two countries could "move on" from the incident.

"It was a cordial, very businesslike conversation between two generals and in the end both of us were committed to working on that issue," he said.

Karzai recently announced a second phase of transition which will see Afghans take charge of six provinces, seven provincial capitals and more than 40 districts, including three in the southern province of Helmand, one of most deadly in the conflict.

Despite the tight timetable, the military and the United Nations disagree over the extent to which violence is really falling in Afghanistan.

The world body said the number of civilians who were killed increased by 15 percent in the first six months of this year.