Afghan forces are likely to face a stiff test with a second round of security transitions from NATO to local control to be announced at a key regional conference next week, experts say.

President Hamid Karzai will declare the impending transfer of up to 17 areas, as plans for Afghanistan to take over security by 2014 move forward, pushed on by Western leaders facing electorates demanding an end to the war.

A first round of handovers took place in July in areas already largely free of US-led NATO forces, but experts say the next phase, for which no timetable has been announced, will prove a bigger task.

The number of areas due for transition is far greater than last time, putting an increasing burden on the still fledgling Afghan security forces even if some of the places are remote with relatively limited Taliban influence.

And while the July handovers were marked by symbolic ceremonies, the second phase comes as the United States and its allies begin to recall troops.

"This time it is more challenging for Afghan forces. They are not well-equipped yet. The enemy has infiltrated their ranks and there are a lot of other problems," said political analyst and author Ahmad Saeedi.

But despite widespread criticism of the Afghan army and police, areas handed over three months ago have generally seen little change in levels of violence, analysts say.

The most watched area, the capital of volatile southern Helmand province, Lashkar Gah, has had five major attacks since transition, which experts say is a similar rate to when it was under NATO control.

Even so the fact that other parts of Helmand are due for the second phase has raised concerns over the "inadequate number of police forces and their poor equipment in the province" said local analyst Abdul Ahad.

Equally, traditional anti-Taliban strongholds in the north of the country have seen increasing numbers of attacks in recent months, including areas moved over in July and other parts due to be trusted to Afghan officials in the next wave.

After the Panjshir valley was handed over it saw its first ever suicide attack last month, targeting the only foreign presence in the area.

And Parwan province, considered generally peaceful and home to Bagram, one of the biggest US-run bases in Afghanistan, was hit this week by a deadly truck bomb, though the governor insists it is ripe for handover.

Karzai is due to announce the areas at the Istanbul Conference next Wednesday, a gathering of regional leaders keen to further peace efforts to end the Taliban-led insurgency after 10 years, the deaths of thousands of troops and civilians, and a war bill of billions of dollars.

The 17 new areas could include seven provinces to be handed over in their entirety: Parwan, Balkh, Daykundi, Nimroz, Samangan, Sar-i-pul and Takhar.

Only some districts of Badakhshan, Badghis, Ghazni, Ghor, Helmand, Herat, Kabul, Laghman, Nangarhar, and Wardak will be moved over to local control.

Kabul city was handed over in 2008, with most of the wider province handed over in July. But the next phase would see the transition of the final district of Sarobi, where French-led forces have been fighting.

In the capital, high-profile attacks including a siege of the US embassy last month and an attack on the British Council in August have shown that the Taliban can still attack anytime, anywhere, said Thomas Ruttig of the Afghan Analysts Network.

"Like we saw in Kabul, which makes the population feel very insecure, that can happen in any place as soon as the insurgent chooses.

"(Transition is) the right thing to do but the first phase also showed what the risks of the handover are in a situation where the ANSF (Afghan national security forces) are not yet there," added Ruttig.

The greatest concern is for the long term, he said, when Afghans have assumed responsibility for large swathes of the country, but "they're not ready and on their own that might be the critical point".

Of the new areas, the most "surprising" was Ghazni, said Ruttig, which has had high levels of Taliban activity. Balkh and Takhar also had some "enclaves" of trouble, he said.