Biden: Afghan leaders, troops need to 'fight for their nation'

US President Joe Biden has urged Afghanistan's leaders to unite and "fight for their nation" against the Taliban insurgents, and said he did not regret deciding to withdraw US troops from the country.

"Afghan leaders have to come together," Biden told reporters on Tuesday. 

"They've got to fight for themselves."

Biden said the United States would continue to support the government in Kabul, but added that "I do not regret my decision" to pull US troops out by August 31 after two decades of war.

US evaluating threat environment

Earlier on Tuesday, State Department spokesperson Ned Price said US is evaluating the threat environment around its embassy in Kabul on a daily basis, when asked about a potential further drawdown from the mission amid a Taliban takeover of eight regional capitals in Afghanistan.

"Obviously it is a challenging security environment. ... We are evaluating the threat environment on a daily basis," Price told reporters in a briefing. 

"The embassy is in regular contact with Washington, with the most senior people in this building, who in turn are in regular contact with our colleagues at the NSC, at the White House."

"But for right now, we've been able to continue those core activities that are important for us to conduct on the ground," Price said, when asked if the worsening security situation was hampering diplomacy.

Taliban solidifies gains 

Taliban insurgents tightened their grip on captured Afghan territory on Tuesday as civilians hid in their homes, and a European Union official said the fighters now control 65 percent of the country after a string of gains as foreign forces pull out.

Taliban seized two more Afghan provincial capitals – including one just 200 kilometres from Kabul - taking the number of major cities to have fallen to the insurgents during the past one week to eight.

Farah city, capital of the same-named province, and Pul-e-Khumri in Baghlan fell within hours of each other, officials in both centres said on Tuesday.

Residents in Pul-e-Khumri reported Afghan security forces retreating toward the Kelagi desert, home to a large Afghan army base.

READ MORE: Why is the Taliban looking unstoppable in Afghanistan?

Several unconfirmed reports said Faizabad, capital of Badakhshan province, also fell to the insurgents late on Tuesday. 

Six of the other provincial capitals to have fallen since Friday are in the country's north with the insurgents setting their sights on Mazar-i-Sharif, the region's biggest city.

Its fall would signal the total collapse of government control in the traditionally anti-Taliban north.

Government forces are also battling the fighters in Kandahar and Helmand, the southern Pashto-speaking provinces from where the Taliban draw their strength.

READ MORE: Taliban seizes two more provincial capitals in Afghanistan

US embassy in Kabul

The United States, due to complete a troop withdrawal at the end of this month that will end its longest war, has largely left the fighting to the Afghans.

The United States on April 27 ordered government employees out of its embassy in Kabul if their work could be done elsewhere, citing increasing violence in the city. 

Price added on Tuesday that the official posture has not changed since then.

"Of course we do want to minimise the number of employees in Afghanistan whose functions can be performed elsewhere," Price said.

READ MORE: What are the possible outcomes of the Afghanistan - Taliban conflict?