NATO insisted Wednesday there was no move towards a speedier withdrawal from Afghanistan despite recent setbacks, including deadly insider attacks, as the alliance prepared for its post-2014 role.

As Washington named a new commander in Afghanistan, NATO head Anders Fogh Rasmussen said the pullout of combat forces by 2014 was on course and that the process would see regular troop drawdowns and redeployments.

"These should not be seen as a rush for the exit," Rasmussen told a press conference at the end of a two-day NATO defence ministers meeting in Brussels.

Any such reading was a "misinterpretation," he said, with such changes the logical consequence of the handover to Afghan forces.

The transition to 2014 was proving a success, with Taliban attacks down in areas now controlled by government forces and home to some 80 percent of the Afghan population, he said.

But among the setbacks which have grabbed headlines in recent months, he noted, have been a spate of so-called "green-on-blue" insider attacks in which renegade local troops have killed more than 50 of their unsuspecting NATO comrades.

The attacks posed a real challenge but "will not work... will not change our strategy," Rasmussen said, amid widespread concern the whole NATO effort in Afghanistan could be compromised as a result.

US Defence Secretary Leon Panetta told NATO ministers that countering such attacks was a key element to ensure success in Afghanistan after almost 11 years of war.

"Whatever motivates these attacks, the enemy intends to use them to undermine mutual trust and cohesion, driving a wedge between us and our Afghan partners.

"We can only deny the enemy its objective by countering these attacks with all of our strength," Panetta said, outlining a series of measures including enhanced training, and greater vigilance and intelligence efforts.

Panetta, who earlier this week voiced frustration with Afghan President Hamid Karzai, said with coalition casualties down and local forces of now some 350,000 troops taking on more of the security burden, NATO had "made significant progress".

Panetta began his address with a reminder that the Afghan war had begun almost exactly 11 years ago in response to the September 11, 2001 terror attacks in the United States.

Rasmussen said ministers agreed NATO could now begin planning plan for its post-2014 role of training and assistance, which he stressed would "not be a combat mission."

To oversee the transition, Panetta announced the nomination of deputy US Marine Corps commander Joseph Dunford to succeed General John Allen as head of NATO forces in Afghanistan.

Dunford will take command of 68,000 US troops who make up the bulk of the coalition force of some 100,000, overseeing the full security handover to Afghan forces and preparing for NATO's training and assistance mission post-2014.

Allen in turn will take over as NATO supreme commander, replacing Admiral James Stavridis to a post traditionally held by a US officer. Both nominations are subject to confirmation by the US Senate.

Ministers began the second day of their meeting Wednesday with a review of Kosovo, where a NATO-led peacekeeping effort is now in its 13th year while there is little sign that the dispute over its self-proclaimed independence from Serbia can be resolved.

Rasmussen said NATO had no plans to change the mission and that its KFOR operation played an "indispensable role" in keeping the peace, adding that he hoped for political progress which could "take the whole region forward".

On Tuesday, the main theme was how to maintain military spending at a time when governments are under pressure on all sides to cut budgets.

The United States accounts for the bulk of NATO defence spending and its portion has increased markedly in the last decade, a sore point for Washington in trying to get its allies to do more.