More than 1,000 Afghan security personnel fled across the border into Tajikistan on Sunday after Taliban advances in northern Afghanistan, the Tajik border guard service said, while dozens of others were captured by the insurgents.

The crossings underscore a rapidly deteriorating situation in the country as foreign troops near a complete withdrawal after 20 years of war in Afghanistan and with peace negotiations stalled.

Hundreds of Afghan security force members have fled swift Taliban advances in the north. But Sunday’s retreats were the largest confirmed, coming just two days after the US officially vacated its main base in Afghanistan as part of a plan to withdraw all foreign troops by September 11.

The Taliban took over six key districts in the northern province of Badakhshan, which borders both Tajikistan and China, following which 1,037 Afghan servicemen fled across the border with Tajikistan’s permission, its border guard service said.

On Sunday, Afghan President Ashraf Ghani spoke to his Tajik counterpart, President Emomali Rakhmon, by phone to discuss the developments.

“Special attention was paid to the escalation of the situation in Afghanistan’s northern areas adjacent to Tajikistan,” the Tajik President’s office said in a statement.

It added that Rakhmon expressed concern about “forced crossings” by members of the Afghan security forces. Tajikistan is looking into setting up camps for potential refugees from Afghanistan, government sources told Reuters.

A senior Afghan official confirmed there had been hundreds of crossings into Tajikistan but did not know the exact number. “The Taliban cut off all the roads and these people had nowhere to go but to cross the border,” he told Reuters on Monday.

Last week, US forces vacated Bagram Air Base — bringing an effective end to the longest war in US history — as part of an understanding with the Taliban, against whom it has fought since ousting the radical Islamist movement from power after the September 11, 2001, al Qaida attacks on the US.

The Taliban has ceased attacks on western forces but continues to target Afghan government and security installations as it makes rapid territorial gains across the country. Peace talks between the two sides remain inconclusive.

Zabihullah Atiq, a parliamentarian from Badakhshan, told Reuters that the Taliban had captured 26 of the border province’s 28 districts — three of which were handed over to the insurgents without a fight.

Afghan security force members used various routes to flee, he said, but added that the Taliban captured dozens of personnel in Ishkashem district where Tajik border forces had blocked any crossing into the former Soviet republic.

Tajik officials said they let in 152 people from Ishkashem, but did not comment on whether anyone was denied entry.

Afghan National Security adviser Hamdullah Mohib, in Moscow on Monday for security talks, said government forces had not anticipated the Taliban offensive but would counterattack.