The UN envoy to Afghanistan on Tuesday warned the country is sliding towards “dire scenarios”.
Taliban militants are making significant gains as the US withdraws its forces ahead of a September deadline, said UN peace envoy Deborah Lyons.
She said the hardliners have fought daily battles with government troops and captured 50 districts since May, when the US began its final exit from a two-decade war.
Talks between the militants and the Afghan government have been gridlocked for months and violence has flared across the nation, prompting fears of the Taliban regaining power and re-imposing an austere version of Islamic law.
“The possible side toward dire scenarios is undeniable,” Ms Lyons told the UN Security Council in New York.
"All of the major trends – politics, security, the peace process, the economy, humanitarian emergency, and of course, Covid – all of these trends are negative or stagnant."
Taliban fighters took control of a key district in Afghanistan's northern Kunduz province on Monday and encircled the provincial capital, police said – the latest significant gain made by the group in recent weeks.
“Most districts that have been taken surround provincial capitals, suggesting that the Taliban are positioning themselves to try and take these capitals once foreign forces are fully withdrawn,” Ms Lyons said.
The Taliban have circulated videos on their website and to WhatsApp groups showing government soldiers who have surrendered being told to return to their homes and receiving money from the fighters.
Taliban leader Mawlawi Hibatullah Akhundzada released a statement on Sunday calling on his fighters to "treat those who surrender well and display good behaviour with them".
Between 2,500 and 3,500 US troops and 7,000 Nato forces remain in the country. The Pentagon says the US troop withdrawal is still on track to conclude by early September.
Talks between the government and the Taliban being held in Qatar have ground to a halt.
Taliban leaders say they are ready to negotiate, but analysts familiar with the talks say the insurgents seem keener to make military gains and bolster their negotiating position.
Fears are growing that the Taliban will regain power and revive strict rules that will clash with the changes that have reshaped parts of Afghan society since 2001.
Before the Taliban were toppled in the US-led invasion after the 9/11 attacks, Afghan girls were banned from school and women accused of crimes such as adultery were sometimes executed.
Estonia's foreign minister Eva-Maria Liimets said the country “has come a long way in the last two decades”.
“Democracy, fundamental freedoms and human rights, especially women’s rights, have become an essential part of the society,” Ms Liimets told the council.
“These achievements must not come under threat.”
Mounting fears and unease about the future has nudged many Afghans to try to leave, including thousands of men and women who fear reprisals because they worked with foreign forces.
US President Joe Biden will host Afghan President Ashraf Ghani at the White House on Friday in talks intended to reaffirm Washington's financial and humanitarian commitment to the Afghan people.