KABUL, Afghanistan - NATO may keep fighting in Afghanistan past its 2014 target date for shifting authority to Afghan forces, the alliance's top civilian in the country said Wednesday.

It was the latest indication that the U.S.-led military operation in Afghanistan will remain sizable well into the next decade, despite plans to draw down troops and transfer responsibility to the Afghan government.

NATO's Mark Sedwill said the end of 2014 was not a deadline. "It's a goal," he told reporters in the capital. "It's realistic but not guaranteed."

U.S. officials have said the handover will start early next year and run through the end of 2014 under a plan set for approval at a NATO summit this weekend in Lisbon, Portugal. Handovers, beginning with a few relatively safe provinces, would hinge on the rearrangement and eventual withdrawal of U.S. and other NATO forces.

The 2014 option has been discussed for some time. But this week's announcements mark the first time officials will outline concrete steps to meet the goal of transferring power in all 34 Afghan provinces within the next four years.

Sedwill said the number of NATO troops -- currently at around 130,000 -- may not be heavily reduced by that date, but the mission will shift to focus on training and advising Afghan troops.

Both the Afghan government and NATO nations have said they're committed to making the transition happen, but they've been hampered this year by increasing violence, with NATO deaths climbing and insurgents expanding attacks to previously peaceful areas in the north and west.

Sedwill said the transition to Afghan control of security will be slow and piecemeal -- often starting with individual districts and building up to the province level. Each area will be evaluated for transfer based on four criteria -- the security situation, the capacity of Afghan security forces in the area, the preparations of NATO forces and the progress toward governance reforms.

As districts are secured, the majority of NATO troops there will be moved to more volatile areas, or turned into trainers, with only a few going home, he said. The idea is that most NATO forces should be trainers or advisers by 2014.

Yet NATO forces may continue to hold some areas years after the 2014 benchmark passes, he said.

"There might still be one or two parts of the country where the transition process is ongoing and that might last into 2015 or beyond," Sedwill said. "This is the point about 2014, it's not an end of mission. It's not even a complete change of mission, but it is an inflection point where the balance of the mission would have shifted."

Two-thirds of all enemy-initiated attacks occur in three provinces -- Kandahar and Helmand in the south and Kunar in the northeast, so those areas will likely be the last to be handed over, NATO officials have said, with 10 Afghan districts accounting for 50 per cent of all the violence.

In addition, specialist strike units that target terrorist operatives are likely to keep conducting operations even after the Afghan government has taken over responsibility, Sedwill said.

He said both 2011 -- the date set for U.S. troops to begin drawing down -- and 2014 are "intermediate milestones" in a larger mission that will last much longer.

The Lisbon summit, which begins Friday, will be the third and largest international meeting on Afghanistan this year as the country's Western allies have come under increasing pressure to provide exit strategies that show timelines for leaving Afghanistan or at least shifting to a mainly training mission.

"We want to build the Afghan leadership so they're taking more and more responsibility for themselves but we recognize it has got to be underwritten by long-term international commitment," Sedwill said.

Neither NATO nor the U.S. have an official "status of forces" agreement -- a pact that sets forth rules and parameters for foreign troops -- with Afghanistan. Sedwill said this document was not the first step toward a status of forces agreement, but a contract that will show NATO's commitment to Afghanistan.

French Defense Minister Alain Juppe described Afghanistan as a "trap" for allied troops. He said in a radio interview with Europe-1 that France had no intention of keeping troops in Afghanistan indefinitely but would not fully withdraw until "Afghan authorities have the situation in hand." France has about 3,850 troops in the country.

Even with the NATO mission appearing to stretch out longer and longer, Sedwill said that the momentum had shifted in NATO's favor.

"It's still clearly fragile. There are significant risks and there will be a long and hard campaign ahead, but we believe that in 2010 we have achieved what we wished to, which is that we've regained the initiative -- having, candidly, lost it in the past few years," Sedwill said.

He said that this was the conclusion of an assessment of the Afghan campaign that he had conducted with Gen. David Petraeus, the top commander of U.S. and NATO forces in Afghanistan.

A spokesman for the NATO military command in Kabul said the international forces intend to keep the pressure up.

"We will carry on and won't lower the intensity. No way," German Brig. Gen. Josef Blotz said.