Afghanistan plans to double the number of elite special forces from 17,000 troops, officials said, part of a long-term strategy to bolster units stretched and exhausted by persistent attacks from Taliban insurgents and other Islamist militants.

Special forces, who represent a small fraction of the 300,000-strong armed forces, have been carrying out nearly 70 percent of the army's offensive operations across the country, underlining Afghanistan's heavy reliance on them.

While regular forces, including police, are deployed largely to defend positions, special forces are taking the battle to militants from Kunduz in the north to Helmand in the south, sometimes working in tandem with U.S. counterparts.

"Our commando forces have to be strengthened and have to be better equipped," Defence Ministry spokesman Dawlat Waziri said.

Waziri declined to give exact numbers, saying only that the special operations division would be increased to the level of an army corps.

But three Afghan and Western officials, speaking on condition of anonymity, said that under current plans, special forces would double and the government was talking to foreign donors about contributing through funding and other assistance.

Recruitment in recent months has focussed on replacing special forces troops lost during last year's fighting, meaning the drive to "substantially" increase numbers would take longer, said NATO coalition spokesman Captain Bill Salvin.

"It's going to take several years to grow to the level that (Afghan President Ashraf) Ghani currently envisions," Salvin said.

Recruitment and training was already underway for more commandos, as well as special forces support units like medical care, intelligence, logistics and communications, he added.

TRUMP'S CALL

On exercises at the Afghan army's special operations training base just outside Kabul, soldiers were confident that they could handle the workload.

"There has been an increase in our operations, but we will keep up our efforts," said Fawad Kamal, a special forces commander. "There hasn't been any interruption."

When they reach the battlefield, newly trained troops will likely be conducting offensive operations, from tracking militant cells to clearing towns seized by insurgents.

"There is a huge need for the number of commandos and special forces to increase in the country," said Mohammed Arif, a new commando recruit. "As long as they are well equipped, they can defend the country very well."

Afghanistan's international allies regularly praise the performance of the special forces, but there is also concern that the workload places them under too much strain.

Last year, the top U.S. commander in Afghanistan, General John Nicholson, discussed plans to strengthen and regenerate the force over the winter months.

At the special forces base, NATO trainers work alongside Afghan instructors, teaching a range of courses from basic shooting and room clearance for new commandos, to advanced leadership courses for the more experienced.

The NATO instructors are part of the Resolute Support mission involving some 13,000 international troops, more than half of them Americans, who train special and regular forces and sometimes advise Afghan troops on the battlefield.

A smaller U.S. counter-terrorism unit is engaged in fighting radical networks including al Qaeda and Islamic State, and often works closely with elite Afghan units in the field.

Nicholson said last month that thousands more advisers would be needed to help prepare Afghan forces to break the "stalemate" in the 15-year conflict, a factor U.S. President Donald Trump must consider when he decides his strategy for Afghanistan.

More than two years after the departure of most international troops, Afghan forces control just 57 percent of the country, compared with 72 percent a year ago, according to SIGAR, a Congressional oversight body.

"A LOT WAS ASKED OF THEM"

The outgoing U.S. military spokesman in Kabul, Brigadier General Charles Cleveland, said Afghan special forces were "the absolute best in this region".

"But by the end of the year they were stretched. An awful lot was asked of them."

Cleveland said any move to boost commando numbers would be factored into coalition deliberations over the future of the international mission.

It peaked at some 100,000 soldiers in 2011, but fell sharply with the intention of eventually handing over control to local forces. A stubborn enemy, lack of resources and high casualty rates among Afghan troops have seen that objective pushed back.

"We'll adjust as we see fit," Cleveland said. "As they (special forces) go into the spring fighting, they are absolutely going to be stronger than where they were in the fall."

NATO is also trying to help the conventional army corps become more effective and relieve pressure on elite units, according to Cleveland.

"The real goal is to get the conventional corps up to the same level of proficiency at their job as the special forces are at their jobs.

"We want these corps to be able to conduct their operations without having to misuse, if you will, the special operations forces."