A Nobel Prize-winning aid group is suspending operations in Afghanistan, after five of its workers were killed in an ambush attack earlier this week.

Vicky Hawkins, a spokeswoman for the relief agency Doctors Without Borders (Medecins Sans Frontieres), told reporters in the Afghan capital that operations would be suspended for "the time being."

"In the coming weeks, we will analyze this event in depth, but for the moment, our priority is to take care of those most affected by this tragedy," she said.

She added that both Afghan and foreign workers of the international aid group would be evacuated from the area where Wednesday's fatal attack took place.

The five aid workers were killed while driving in northwest Afghanistan, by unknown assailants wielding assault rifles and grenades. Along with two Afghans, the victims include a Norwegian, a Belgian and a Dutch national.

The incident marks one of the worst attacks on relief workers in Afghanistan since the 2001 war that overthrew the country's former Taleban regime.

Local officials attributed the killings to Taleban militants, who have been conducting armed attacks against Afghan targets, as well as foreign aid groups and the U.S. military. In addition, a claim of responsibility was made by a man identifying himself as a Taleban fighter.

Most of the Taleban's activity has been confined to the east and south of the country. Wednesday's killings, however, took place in the remote northwest, near the border with Turkmenistan.

The U.N. special envoy to Afghanistan, Jean Arnault, condemned the killing of the aid workers. U.N. spokesman Manoel de Almeida e Silva cited Mr. Arnault's recent report to the Security Council, warning that Afghanistan is becoming more dangerous.

"Mr. Arnault stressed that security in the country remains insufficient. He noted that in recent months, the situation had, in fact, evolved negatively," he said.

Mr. Arnault called for the international community to increase its military commitment to Afghanistan.

The country hosts about 20,000 U.S. forces and more than 6,000 international peacekeepers, along with Afghan military units.