NATO soldiers stand near a damaged NATO military vehicle at the site of a suicide car bomb blast in Kabul, Afghanistan, October 11, 2015. REUTERS/Omar Sobhani

By Krista Mahr and Sabine Siebold

KABUL/ZARAGOZA, Spain (Reuters) - NATO partners are considering ways of beefing up their training and assistance mission in Afghanistan as concern grows over the ability of local forces to fight an escalating insurgency by Taliban militants, according to officials in Brussels and Kabul.

The Taliban's success in seizing the northern city of Kunduz in late September and holding it for several days caused shock among Afghanistan's international partners, who have invested billions of dollars trying to create a security force capable of standing on its own.

"The situation is sobering, it is not as stable as we hoped it would be," said General Hans-Lothar Domroese, a veteran of Afghanistan who is Germany's second-most senior general in the NATO alliance.

Speaking at the margins of a NATO exercise in Spain, he said weak government control in many areas and corruption were making the job of reinforcing security more difficult, but added: "If we don't stay, they will drift into a maelstrom, and there is a significant danger that they get torn away."

Ministers from NATO countries are due to meet in early December to decide on the future of Resolute Support, the non-combat NATO-led mission launched in January to train, advise and assist the Afghan government and security forces.

Formally the NATO-Afghan agreement is open-ended, but in practice its future depends on member countries' willingness to commit troops and resources.

"CAN'T HELP FOREVER"

Officials describe a sense of fatigue and doubt about the strategy of the coalition of NATO partners and allies following Washington's announcement it would extend troop levels through most of 2016 due to worsening security.

"Nobody is pleased with the progress," said one NATO diplomat in Brussels, who spoke on condition of anonymity. "The alliance's forces can't keep helping forever ... Right now we are helping them more than we'd like."

However, no one Reuters spoke to expected a major overhaul of the mission, or suggested NATO members would send additional troops back to Afghanistan or return to combat.

There are fewer than 14,000 coalition troops in the country, compared to around 140,000 a few years ago.

Previous plans to reduce the numbers further appear to be on hold, and several nations have signaled they will extend their troop levels along with the United States.

National Security Council spokesman Tawab Ghorzang said the Afghan government was happy with Resolute Support, which had proved "very successful".

"We hope that our friendly nations, especially the RS mission, continue their support till the elimination of terrorism threats in Afghanistan," he said in a statement.

But after 14 years of fighting, with more than 3,000 coalition dead, there is little appetite in Western countries for deeper military involvement in Afghanistan.

"We will not go into a new combat operation," NATO Secretary General Jens Stoltenberg told reporters recently.

At the same time, the tens of thousands of refugees heading to Europe has highlighted one of the results of letting the country slide into anarchy, leaving governments with little choice but to try to make the mission work better.

"ROBUST ADVICE"

"Robust advice is what we need," Domroese said, adding that as well as improved close air support, thought should be given to giving Afghan forces more access to intelligence and surveillance data held back under existing rules.

"If I can see there is somebody coming around the corner and I can't tell the Afghans, can't enable them, then you may have to tackle this issue again politically and rethink Resolute Support," Domroese said.

Afghan officials have repeatedly pleaded for help in areas like close air support when forces come under attack by the Taliban, but a lack of equipment and trained personnel has made strengthening the tiny air force difficult.

However, some Western officials express scepticism about the value of extending a mission to support an ill-paid, sometimes demoralized security force riddled with corruption.

"After 14 years, do you really think that 12 more months is going to make a difference?" said a Western official. "The strategy is flawed. We're building and funding the wrong army."

He said the Afghan government cannot afford to build a security force of 352,000, its target strength, or even one much smaller. At present, the international community funds more than 90 percent of Afghan security forces' operating costs.

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