The United Nations refugee agency, UNHCR, is withdrawing its workers from
southern and eastern Afghanistan.
Afghan refugees from Pakistan could be worst hit by the closures
The announcement follows the killing of a 29-year-old French UNHCR employee, Bettina Goislard, in the eastern town of Ghazni on Sunday.
There have been conflicting reports that her attackers belonged to the Taleban militia, ousted two years ago.
A resurgence in support for the radical
Islamic movement has been blamed for spiralling violence in Afghanistan.
Ms Goislard was the first foreign UN employee to have been killed in Afghanistan since a US-led invasion drove the Taleban out of the capital, Kabul, in 2001.
Fears that more workers could be attacked have prompted the UNHCR to withdraw 30 of its non-Afghan staff in four provinces bordering Pakistan in the south and east of the country.
A UN spokesman said the move was temporary.
"We will review the situation in two weeks," said Filippo Grandi, the UNHCR's mission chief in Afghanistan.
He said reception centres for refugees in the provinces of Nangarhar, Paktia, Khost and Kandahar would be closed down.
The BBC's Kabul correspondent, Crispin Thorold, says
tens of thousands of refugees could be hit by the closures - most of them Afghans returning from Pakistan.
Ms Goislard, a 29-year-old French national, had previously worked for the UNHCR in Rwanda and Guinea.
Ms Goislard died of gunshot wounds in her car on Sunday
Motorcycle-borne assailants shot her dead while she was being driven in a UN vehicle in Ghazni on Sunday.
The gunmen are now in custody and say they were working for the Taleban, according to local officials.
Mullah Abdul Samad, a high-ranking Taleban official, confirmed this, telling Reuters news agency: "Our guerrillas were involved."
He added that Western aid workers, journalists and their Afghan employees were all legitimate targets.
However, Mullah Akim Latifi, another senior Taleban official, denied any link to Ms Goislard's killers.
Mr Latifi told Associated Press the movement was "not interested in killing aid workers".
"We only want to kidnap them to bargain for the release of our jailed comrades," he said.
He confirmed the Taleban hope to exchange a Turkish engineer they kidnapped on 30 October for comrades jailed by the Afghan Government.
Aid agencies feel the heat
Correspondents say remnants and new recruits of the Taleban are trying to force foreign aid agencies out of eastern Afghanistan to secure the region for opium cultivation and hardline Islamic rule.
UN staff in Afghanistan have been temporarily told to stay indoors
They say the attacks on UN workers and property may be inspired by the example of guerrillas in Iraq who have hampered US reconstruction efforts by bombing aid agencies.
Last Tuesday, a car bomb exploded outside a United Nations office in Kandahar.
No one was killed or injured in that blast, which damaged windows and barriers around the building.
On Sunday, three UN employees in Paktia Province also narrowly escaped injury after a remote-controlled bomb blew up near a vehicle they were travelling in.