KABUL - The United Nations special envoy to Afghanistan held face-to-face meetings with three powerful northern warlords Saturday to protest what an aid official called the "alarming level of violence" directed at foreign aid groups in the area including a particularly vicious rape.

UN envoy Lakhdar Brahimi met with the country's deputy defense minister and Uzbek warlord Abdul Rashid Dustom, Dustom's rival General Atta Mohammed, and Hazara leader Haji Mohammed Muhaqiq, all of whom are delegates to the on-going Loya Jirga Tribal Council in Kabul, the German news agency, DPA reported from Kabul.

He informed them of the incidents in Balkh Province, some of which a UN spokesman described as "pre-planned and organized", and demanded better security for foreign aid workers.

Brahimi told the warlords that "whatever the actions (taken), they must be visible actions," said UN spokesman Manoel de Almieda e Silva.

"The leaders of the three main factions in the north promised to take urgent measures as required by this grave situation," Almieda e Silva said.

The meeting comes a day after a truck transporting bread to a camp of internally displaced people came under light arms fire that critically injured an Afghan aid worker. The aid group has now withdrawn from the country and has no plans to return.

"Other NGOs are considering similar actions as a result of the situation in that part of the country," Almieda e Silva said.

On June 8, a group of seven soldiers stopped a vehicle carrying a foreign aid worker and local staff working for a small non governmental organization in Mazar. They beat up the Afghan men and gang raped the woman, who has since been evacuated from the country.

In the intervening week, an estimated $150,000 worth of equipment has been stolen in three separate armed robberies of foreign relief workers in their offices and vehicles in the city.

Spokesman Almieda e Silva said the daylight armed robberies appeared "pre-planned and organized".

On Thursday, an international clinic in the town of Sholgara was "directly targeted" by gunmen during factional fighting between troops loyal to Dostum and Atta Mohammed. A consultation room and observation room were riddled with bullets during the fighting but no one was injured.

None of the agencies that have been hit by the recent wave of lawlessness have been publicly identified.

International agencies in Mazar today agreed to send a formal letter to the local authorities and the warlords, meet with community leaders and contact the recipients of their aid to "prepare them for the possible suspension of assistance in the event the security situation does not improve", the spokesman said.

This is the second time in as many months that the UN has received assurances from factional leaders that they would crack down on violence directed at aid workers.

In April, an Afghan employee of the UN Food and Agriculture Commission was murdered by local gunmen in Mazar, the most serious in a series of beatings and acts of rape and extortion blamed on troops loyal to Dostum and Atta Mohammed.