Some 30 foreign staff members are being withdrawn, and refugee centers in the Afghan provinces of Nangarhar, Paktia, Khost and Kandahar are being closed.
"We are taking today a painful decision to temporarily reduce staff in the eastern and southern province," said Filippo Grandi, the chief of mission in Afghanistan with the United Nations High Commissioner for Refugees. "We will review the situation after two weeks."
A day earlier, the U.N. refugee agency barred staff from traveling by road in Afghanistan. "We certainly cannot allow our staff to be left at the mercy of those who are targeting us," said Grandi.
The precautions follow a series of attacks on the United Nations in recent days, including the killing of Bettina Goislard, a 29-year-old refugee agency worker, as she traveled through a bazaar in the city of Ghazni, 60 miles southwest of the capital.
That same day saw a bomb attack on a U.N. vehicle in eastern Paktia province. And on Nov. 11, a car bomb exploded outside U.N. offices in Kandahar, injuring two people.
Several international aid organizations operating in the south also held an emergency meeting to discuss "options which may include the withdrawal from the southern region of Afghanistan," according to ACBAR, an umbrella group of 86 aid agencies working in Afghanistan.
The group quoted Anne Wood, a senior coordinator for Portland, Oregon-based Mercy Corps, as saying: "The situation continues to deteriorate. We do not believe that measures taken so far ... will effectively address the deepening crisis. In the south, we are now at a critical juncture."
The attacks against the United Nations and its workers in Afghanistan have sent a shudder through the international community, raising fears the world body could be emerging as a target of choice for suspected Taliban insurgents.
Though aid workers have been targeted increasingly in Afghanistan in recent months, the concentration of attacks against the United Nations in the past week was unprecedented.
In response, the United Nations on Monday suspended humanitarian operations in southern and eastern Afghanistan. U.N. associate spokeswoman Marie Okabe said staff would continue working in the north, which includes the capital, Kabul.
Goislard, a Frenchwoman, was the first international U.N. worker killed in Afghanistan since the Taliban fell in late 2001. She had been traveling in the town of Ghazni when two motorcycle-riding assailants shot her to death. Her Afghan driver was wounded; another Afghan colleague was unhurt.
"It's pretty clear that it was a targeted attack. It was a clearly marked U.N. vehicle. She was obviously an expatriate and she was very well known in the community, because she was very active," said Maki Shinohara, the UNHCR spokeswoman in Kabul. "This was done by someone who really wants to undermine all our efforts to build peace in this country."
Goislard's parents will be planning to travel to Afghanistan to retrieve her daughter's body. Shinohara says Goislard had told colleagues that if anything happened to her, she wished to be buried in Afghanistan, but that decision will be left to her parents.
A Western security official who spoke to The Associated Press on condition of anonymity says there are strong indications the three recent attacks were coordinated, marking a sea change in the already dismal security situation in Afghanistan.
Moments after the attack on Goislard, police fired on the motorcycle, wounding one of the Afghan assailants and arresting both. Afghan officials say they are supporters of the ousted Taliban regime.
Taliban insurgents also claimed responsibility for the Kandahar car bombing, which wounded two people. On Sunday, a remote-controlled bomb exploded near a U.N. vehicle carrying three Afghan employees in Paktia province; no one was injured.
Analysts say the ousted regime is trying to undermine development work and force aid groups out of Afghanistan.
"You do this to get rid of the international community," said Vikram Parekh, a senior analyst on Afghanistan for the International Crisis Group. "If these agencies pull out because of these attacks, reconstruction work will not get not done and ... alienation among the local population to the international community will set in."
The Western security official said Afghan insurgents could be watching and mimicking events in Iraq, where the United Nations has become a target after the U.S.-led war. A suicide truck bomber struck U.N. headquarters in Baghdad on Aug. 19, killing 23 people. A suicide bomber killed an Iraqi policeman in a subsequent attack on the same building.
"It would be underestimating the intellect of the enemy to think they are not influenced by outside events, including in Iraq. Just like us, they are observing, adapting and learning," he said.
The brutal tactics appear to be working.
The United Nations has pulled most of its staff out of Iraq because of security concerns. In Afghanistan, attacks have forced many aid agencies to suspend work in wide swaths of the country.
After Sunday's killing, the UNHCR ordered a standdown of staff nationwide, with workers told to remain in their offices until further notice. The refugee agency also said in a statement that it was temporarily closing two repatriation centers inside Pakistan that help Afghan refugees about to return home.
A U.N.-wide review of security is under way, though the world body vowed it would never be forced out of Afghanistan.
"They attack us - fine. It's not going to stop us," said David Singh, a U.N. spokesman in Kabul. "We will definitely not be intimidated by these people. The United Nations is here to stay in every part of the country."