Overstretched Afghan forces are pulling back from violent southern districts without a fight, ceding key territory to the resurgent Taliban as part of an unprecedented "strategic retreat" that has stoked fears government control is slipping.

Beset by record casualties, desertions and troop shortages, Afghan troops have recently abandoned outposts in parts of central Uruzgan province, extending a withdrawal which began last month.

They have already pulled out of Musa Qala and Nowzad districts in neighbouring Helmand, bastions that foreign troops struggled for years to defend as the opium-rich region teeters on the brink of collapse.

The retreat has triggered fevered speculation about possible government backroom deals with the Taliban at a time when international efforts are growing to bring the insurgents to the negotiating table.

"Once you start pulling out troops and surrendering hard-won territory, you are basically admitting that the Taliban have won," said Mohammad Ismail, a tribal elder from Musa Qala who fled the area after government troops pulled out.

"This is a betrayal to all those who have sacrificed their lives to defend these areas over 15 years."

The withdrawal, which comes as Afghan forces struggle to fight off the increasingly bloody insurgency, has sparked concerns that the government is fast losing control of volatile Helmland.

The Taliban effectively control or contest at least 10 of the 14 districts in Afghanistan's biggest centre for opium production, a lucrative source of insurgent funding which makes the province a hotly contested area.

- 'Effectively a surrender' -

But Afghan commanders dismiss claims of any Taliban deal, describing the recent withdrawals as a "tactical" manouevre aimed at consolidating forces from isolated, hard-to-defend areas.

"Those who are criticising the plan do not know the art of war," defence ministry spokesman Dawlat Waziri told AFP.

"We are not withdrawing from Helmand; Afghan forces are being redistributed in order to mount more effective offensives against the enemy."

Many of the hundreds of withdrawn forces have been redeployed to beef up a security belt around Lashkar Gah, Helmand's capital which recently came close to falling to the Taliban, officials said.

But many experts reject government claims that the withdrawal qualified as a "strategic retreat".

"This new strategy is effectively a surrender to the Taliban. That's because there's no reason to think that this territory will be taken back anytime soon," said Michael Kugelman, Afghanistan expert at Washington-based think tank the Woodrow Wilson International Center for Scholars.

"A strategic retreat suggests that at some later point Afghan forces will return to reengage the Taliban and take back control.

"Afghan forces are overstretched and under-resourced. I can't see them being in a position to win back these areas."

- 'Defend everywhere, defend nowhere' -

The plan reflects a longstanding demand from NATO, which has been advising Afghan forces -- stretched thin across multiple fronts across Afghanistan -- to reduce its footprint around the country.

"They (Afghan forces) have got too many checkpoints and they've got too many of their forces strung out on checkpoints," US military spokesman Brigadier General Wilson Shoffner told reporters in January.

"There's an old military saying that if you defend everywhere, you defend nowhere, and this is particularly true in Afghanistan."

Shoffner said the Afghan national army faces a huge manpower shortfall of about 25,000, making it necessary to cut back some outposts.

Government forces, which have been fighting without the full support of NATO since its combat mission ended in December 2014, are expected to abandon more checkpoints as fighting intensifies amid faltering peace efforts.

Last year was a record for civilian casualties, according to the UN, which reported 11,000 civilian casualties in 2015 including 3,545 deaths -- the most since the agency began tabulating the statistics in 2009.

The Taliban on Saturday refused to hold direct peace talks with the Afghan government, dealing a blow to international efforts to revive negotiations aimed at ending their 14-year insurgency.

But the new strategy does not factor in a crucial element -- the plight of the local population.

"The Taliban are hunting down residents who worked for the government," said Abdul Ahad, a local elder in the Kharkhord area of Uruzgan, from where dozens of Afghan troops recently pulled out.

"Government soldiers left us here to die," he told AFP by telephone from the area, which is home to some 20,000 families.