Afghan government plans to boost army and police numbers massively have been greeted with scepticism by diplomats and military experts who say the figures are too ambitious.

Afghanistan lacks the capacity to recruit and train men in large enough numbers, they said, despite a pledge by President Hamid Karzai to take over the nation's security from foreign troops by the end of his new five-year term.

Defence Minister Abdul Rahim Wardak used a ceremony on Saturday in Kabul, where NATO took over command of Afghan army training from the United States, to announce that security force numbers would be cranked up to 400,000.

"Our programme is to have a total of 240,000 soldiers," ministry spokesman Zahir Azimi told AFP, more than double the current total of about 100,000.

The hope is to have 150,000 by the end of next year, he added, with the rest "in following years".

Police numbers would rise to 160,000 from the current 97,000, said Zamarai Bashary, interior ministry spokesman, with the deadline "under discussion".

Experts said recruiting such numbers would be difficult because Afghanistan lacks a pool of literate young men, as well as veterans with leadership skills, facilities for training and grooming, and money for weapons and ammunition.

"That means they will have to be raising trained soldiers at a rate of 3,000 people per month -- that's a very tall order," said a military attache in Kabul, speaking on condition of anonymity.

"They will have to find more than 100,000 at least semi-educated young men who are volunteers to join the army. It will be difficult," he said.

Afghanistan's first batch of 120 officers passed out earlier this year after four years' training at the National Military Academy.

NATO said that 800 troops, or three companies, graduated from an accelerated combat-training programme on Sunday, taking the Afghan army a "step closer to meeting its goal" of extra troops.

After their five weeks of training, the forces would be deployed across the country, NATO's International Security Assistance Force (ISAF) said.

Increasing police numbers involved similar problems to the army, said a Western diplomat, speaking anonymously.

Wardak spoke "prematurely," he said, as interior ministry working groups are yet to complete reports on which such decisions will be based.

"There is no way we can recruit that many people," the diplomat said.

"The numbers are political. The Afghans are under pressure from the United States to boost the numbers, but the Afghans are also putting on the pressure for support to do so."

Western allies are pressuring Karzai to bolster security forces and take responsibility for the war, now into a ninth year against Taliban-led insurgents, so their own forces can be drawn down.

Afghan defence forces are backed by more than 100,000 NATO and US soldiers taking the operational lead in battling the insurgents, who are spreading their footprint across the country.

The United States and NATO are eager to cut deployments in response to Western public opinion, which increasingly wants troops to return home.

US President Barack Obama is considering a large increase in US troop numbers, expected to be announced after Thursday's Thanksgiving holiday and to include a component of trainers.

General Stanley McChrystal, US and NATO commander in Afghanistan, has adopted a strategy called "partnering" in which Afghan and foreign soldiers train, live and fight together.

But NATO commanders, who last month approved a plan to accelerate the training programme, said the Afghan army is plagued by desertions and drug addiction.

Out of the some 94,000 Afghan soldiers trained so far, 10,000 have deserted, said General Egon Ramms, commander of the operational headquarters in charge of ISAF. Some 15 percent are drug addicts, he said.

The police, one member of which shot dead five British soldiers this month, are prone to corruption and their training has been inefficient, he said.

McChrystal plans to double the size of the Afghan police within a few years. Their losses are expected to reach 1,500 killed this year, and some 10,000 are AWOL.