Afghan First Vice President Amrullah Saleh said on Twitter Tuesday that he is in the country and is the "legitimate caretaker president" as the Taliban took control of Afghanistan and a transitional government is formed.

"Clarity: As per the Constitution of Afghanistan; in absence, escape, resignation or death of the president; the FVP (first vice president) becomes the caretaker president," he said.

"I am currently inside my country and I am the legitimate caretaker president," Saleh added.

"I am reaching out to all leaders to secure their support and consensus," he declared.

Saleh had said after a security meeting chaired by then President Ashraf Ghani last week that he was proud of the armed forces and the government would do all it could to strengthen resistance to the Taliban.

Earlier, Saleh also vowed that "he will not surrender."

In a report, Agence France-Presse (AFP) said that the FVP has retreated to the country's last remaining holdout, the Panjshir Valley northeast of Kabul.

"I won't disappoint millions who listened to me. I will never be under one ceiling with (the) Taliban. NEVER," he wrote in English on Twitter Sunday, before going underground.

A day later, pictures began to surface on social media of the former vice president with the son of his former mentor and famed anti-Taliban fighter Ahmed Shah Massoud in Panjshir – a mountainous redoubt tucked into the Hindu Kush.

Saleh and Massoud's son, who commands a militia force, appear to be putting together the first pieces of a guerilla movement to take on the victorious Taliban, as fighters regroup in Panjshir.

'Resist with all our might'

Famed for its natural defenses, the valley never fell to the Taliban during the civil war of the 1990s, nor was it ever conquered by the Soviets a decade earlier.

"We will not allow the Taliban to enter Panjshir and will resist with all our might and power, and fight them," one resident told AFP on condition of anonymity.

Such a battle would be the latest in Saleh's long struggle against the Taliban as a onetime insurgent turned spy chief and later vice president.

Orphaned at a young age, Saleh first fought alongside guerilla commander Massoud in the 1990s. He went on to serve in his government before being chased out of Kabul when the Taliban captured it in 1996.

The hardliners then tortured his sister in their bid to hunt him down, Saleh has said.

"My view of the Taliban changed forever because of what happened in 1996," Saleh wrote in a Time magazine editorial last year.

'We will continue our fight'

After the Sept. 11, 2001, terrorist attacks, Saleh – then a part of the anti-Taliban resistance – became a key asset for the CIA.

The relationship paved the way for him to lead the newly formed Afghanistan intelligence agency, the National Security Directorate (NDS), in 2004.

As NDS chief Saleh is believed to have amassed a vast network of informants and spies inside the insurgency and across the border in Pakistan, where Pashto-speaking agents kept track of Taliban leaders.

The intelligence Saleh gathered provided what he alleged was proof the Pakistani military continued to back the Taliban.

Saleh's rise however has not been without its share of dramatic stumbles.

In 2010, he was sacked as Afghanistan's spy chief following a humiliating attack on a Kabul peace conference.

Exiled into the political wilderness, Saleh maintained his fight against the Taliban and Islamabad on Twitter, where he fired off daily tweets taking aim at his longtime foes.

A return to favor came in 2018 when he briefly oversaw the interior ministry after sealing an alliance with President Ashraf Ghani, who has now fled to an unknown location.

Saleh went on to become the former leader's vice premier.

His most recent political revival came as the United States was preparing to exit Afghanistan and coincided with a series of assassination attempts on Saleh by the Taliban. His latest close call came last September when a massive bomb targeting his convoy killed at least 10 people in Kabul.

Within hours of the attack, Saleh appeared in a video with his left hand bandaged, promising to fight back.

"We will continue our fight," he said.

The Taliban declared the war in Afghanistan over after taking control of the presidential palace in Kabul while Western nations scrambled Monday to evacuate their citizens amid chaos at the airport as frantic Afghans searched for a way out.

Afghan President Ashraf Ghani said Sunday, "The Taliban have won with the judgment of their swords and guns, and are now responsible for the honor, property and self-preservation of their countrymen," after fleeing the country as the militants entered the capital virtually unopposed, saying he wanted to avoid bloodshed. The ensuing hours saw hundreds of Afghans desperate to leave flood the Kabul airport.

"Today is a great day for the Afghan people and the mujahideen. They have witnessed the fruits of their efforts and their sacrifices for 20 years," Mohammad Naeem, the spokesperson for the Taliban's political office, told Qatar-based media outlet Al-Jazeera TV. "Thanks to God, the war is over in the country," he said.

It took the Taliban just over a week to seize control of the country after a lightning sweep that ended in Kabul as government forces, trained for two decades and equipped by the United States and others at a cost of billions of dollars, melted away.