Afghan security forces will soon take over responsibility for the whole of the country, officials said Saturday, a major milestone as the NATO-led war effort winds down after 12 years of fighting.

The handover of the last 95 districts from NATO to Afghan forces includes many of the most volatile areas of south and east Afghanistan where the Taliban have fought a bloody insurgency against the US-backed government since 2001.

NATO and Afghan officials, who declined to be named, said that President Hamid Karzai would attend a ceremony within days to mark a key point of the "transition process" to full Afghan sovereignty.

The exact date and location of the handover has not yet been announced, but it will complete a programme started in 2011 when relatively-peacefully areas inhabited by about 20 percent of the population were put under Afghan security.

"The event will be held shortly and 95 districts in 11 provinces are included in the fifth and final phase. Further details will be released later for security reasons," an Afghan government official told AFP.

The last "tranche" of districts includes 13 in Kandahar province, the birthplace of the Taliban, and 12 in each of Nangarhar, Khost and Paktika provinces -- all hotbeds of insurgent activity along the border with Pakistan.

After the handover, 100,000 NATO forces will only play a supporting and training role as Afghan soldiers and police take the lead in the fight against the militants who were ousted from power after the 9/11 attacks.

However doubts remain over the ability of the 350,000-strong Afghan forces to thwart the Taliban, and the NATO military coalition will retain an important role in logistics and air support as well as in combat when required.

The Afghan army has suffered a sharp rise in casualties as it has taken on more frontline fighting, and it is also undermined by a high desertion rate that means thousands of new recruits are needed each month to fill its ranks.

Completion of the security handover "is one of the very important issues for Afghanistan," Masoom Stanikzai, head of the High Peace Council secretariat that is leading efforts to open talks with the Taliban, told reporters.

"One of the biggest excuses that enabled the Taliban and other groups to mobilise fighters was the notion that Afghanistan was occupied by foreign forces who would stay for ever.

"The inspiration for fighting is gradually changing to a roadmap for peace. It is a very gradual shift... but there are changes emerging in different parts of the country."

On Friday, NATO commander General Joseph Dunford expressed concern that progress made in Afghanistan since 2001 could be under threat if donor nations cut back support.

"The gains that we have made to date are not going to be sustainable without continued international commitment," he said.

Recent attacks have demonstrated the Taliban's ability to strike at Kabul as the country prepares for next year's presidential elections and the NATO withdrawal by the end of 2014.

A suicide car bomb on Tuesday killed 15 civilians outside the Supreme Court, an attack that came a day after gunmen fired grenades at the city airport, while an international aid group's compound was targeted in a seven-hour battle late last month.

Despite the attacks penetrating the capital's defences, the effective response of elite Afghan security forces has been widely hailed as a sign of increasing professionalism.