Taliban fighters sit on a vehicle along the street in Jalalabad province on Sunday. AFP/VNA Photo

 KABUL — The Taliban were on the brink of total victory in Afghanistan on Sunday, with their fighters ordered to wait on the outskirts of the capital and the government conceding it was preparing for a "transfer of power".

Militants surrounded Kabul following an astonishingly quick rout of government forces in recent days, with troops incapable of holding onto territory without US military support.

The fall of Kabul will see the hardline Islamic group take back power two decades after US-led forces toppled it in the wake of the September 11, 2001 attacks.

"The Islamic Emirate instructs all its forces to stand at the gates of Kabul, not to try to enter the city," a spokesman for the Taliban tweeted as residents reported insurgents on the outskirts of the city.

"Until the completion of the transition process, the responsibility for the security of Kabul is with the other side (the Afghan government)".

The United States began moving its citizens and Afghan staff to Kabul airport, with the help of thousands of troops deployed to the capital to assist with the evacuation.

The Taliban's imminent takeover triggered fear and panic in Kabul among residents fearful of the group's hardline brand of Islam.

The Afghan government signalled earlier there were negotiations underway to avoid bloodshed in Kabul, and to hand power to the Taliban.

"The Afghan people should not worry... there will be no attack on the city and there will be a peaceful transfer of power to the transitional government," Interior Minister Abdul Sattar Mirzakwal said in a recorded speech.

Afghan President left the country

President Ashraf Ghani -- who is widely expected to resign – is said to have left the country on Sunday, hours after the Taliban ordered its fighters to wait on the outskirts of the capital following an astonishing rout of government forces.

"The former Afghan president has left the nation," Abdullah Abdullah, who heads the peace process, said in a video on his Facebook page.

Earlier Ghani in a video message released to media urged what remains of his security forces to maintain law and order.

There are fears of a security vacuum in the capital as thousands of police and other armed services members have abandoned their posts, uniforms and even weapons.

"It is our responsibility and we will do it in the best possible manner," Ghani said, hours after the Taliban seized two nearby prisons and released thousands of inmates.

Suhail Shaheen, based in Qatar as part of the Taliban's negotiating team, said the group wants a swift takeover.

"In next few days, we want a peaceful transfer," he told the BBC.

Evacuations

The scale and speed of the insurgents' advance have shocked Afghans and the US-led alliance that poured billions into the country over the past two decades.

President Joe Biden ordered the deployment of an additional 1,000 US troops to help secure the emergency evacuation from Kabul of embassy employees and thousands of Afghans who worked for American forces and now fear Taliban reprisals.

That was on top of the 3,000 American soldiers deployed in recent days, and 1,000 left in-country after Biden announced in May that the final withdrawal of the US military presence in Afghanistan would be completed by September 11.

That decision has come under increased scrutiny given the collapse of the Afghan armed forces, but he insisted Saturday there was no choice.

"I was the fourth president to preside over an American troop presence in Afghanistan -- two Republicans, two Democrats. I would not, and will not, pass this war onto a fifth," Biden said.

Ghani's government was left completely isolated on Sunday after the insurgents overran the anti-Taliban northern stronghold of Mazar-i-Sharif and the eastern city of Jalalabad.

Like with most of the other captured cities, the seizure of power came after government forces surrendered or retreated.

Videos posted on pro-Taliban social media accounts showed the group's heavily armed fighters in cities across the country, waving white flags and greeting locals.

Most of the fighters appeared young, suggesting they were most likely infants or unborn when the Taliban was toppled from power in 2001. AFP