KABUL: The Taliban plan to present a written peace proposal to the Afghan government side as soon as next month, a spokesman for the Islamist insurgents said even as they make major territorial gains in the breach left by departing foreign forces.

Hundreds of Afghan security force members have fled into neighbouring Tajikistan in the face of Taliban advances since the United States vacated its main Afghan base, centrepiece of U.S. and NATO might for almost two decades in the country, as part of a plan to withdraw all foreign troops by Sept. 11.

While the transfer of Bagram Air Base to the Afghan army added momentum to a Taliban drive to seize control over new districts, Taliban leaders renewed the long stalled talks with Afghan government envoys in Qatar's capital Doha last week.

"The peace talks and process will be accelerated in the coming days...and they are expected to enter an important stage, naturally it will be about peace plans," Taliban spokesperson Zabihullah Mujahid told Reuters on Monday.

"Possibly it will take a month to reach that stage when both sides will share their written peace plan," he said, adding that the latest round of talks were at a critical juncture.

"Although we (Taliban) have the upper hand on the battlefield, we are very serious about talks and dialogue."

The upsurge in fighting and the flight of thousands of members of the tattered Afghan security forces have raised grave doubt about the U.S.-backed peace negotiations, which began last year under the then-President Donald Trump's administration.

Western security officials said Taliban forces have captured more than 100 districts but the Taliban say they have control of more than 200 districts in 34 provinces comprising over half the Central Asian country.

On Sunday, more than 1,000 Afghan security personnel retreated across the northern border into Tajikistan after Taliban advances, the Tajik border guard service said, while dozens of others were captured by the insurgents.

Najia Anwari, spokeswoman for Afghanistan's Ministry for Peace Affairs, confirmed that intra-Afghan talks had resumed and said its representatives were "very happy" that Taliban envoys were rejecting the process outright.

"It is difficult to anticipate that the Taliban will provide us with their written document of a peace plan in a month but let's be positive. We hope they present (it) so as to understand what they want," said Anwari.

Last month the head of Afghanistan's official peace council called for the long halting talks on a settlement to decades of devastating violence should not be abandoned despite surging Taliban attacks.

Last week U.S. forces vacated Bagram Air Base as part of an understanding with the Taliban, against whom it has fought since the Sept. 11, 2001 attacks on the United States.