By Ian MacWilliam
BBC correspondent in Kabul
The United Nations has suspended road travel in parts of southern Afghanistan following a spate of attacks on Afghan aid workers and policemen by unidentified assailants.
A resurgent Taleban movement has been attacking government targets and those connected with foreign aid organisations in the south-east of the country in recent months.
The UN announcement comes as Nato takes over security in Kabul
The worsening situation in the south comes as Nato is about to take over leadership of the international security force in the capital on Monday.
The UN announcement follows three attacks in recent days.
Ten Afghan workers for a local aid organisation were severely beaten in a district of Kandahar province last week when they refused to hand over the keys to their vehicles.
On the same day, five policemen were wounded in the same district, when men armed with rocket-propelled grenades and heavy machine guns attacked their checkpoint.
Also last week, six government soldiers and a driver for an American aid organisation were killed in the neighbouring province of Helmand.
UN missions have now been ordered to avoid travel in parts of Kandahar and Helmand provinces and in all of Uruzgan and Zabul.
These travel restrictions will limit the work of UN supported reconstruction and aid projects in rural areas of the south.
These provinces were the heartland of the Taleban movement.
Their renegade leader, Mohammed Omar, is still at large, possibly hiding in the mountainous interior of this part of Afghanistan.
The attacks come amid growing concern about security in Afghanistan.
Nato is to take over control of Isaf, the international security force for Kabul, on Monday, when Germany and the Netherlands complete six months leading the force.
But Isaf has no mandate to operate outside the capital.
There have been repeated demands for an extension of Isaf operations beyond Kabul, but military observers say there is no nation willing to supply the extra troops such an extension would require.