The OSCE was due to send a total of 2,000 verifiers to the Serbian province, but only about 800 are currently deployed on the ground.

The agreement reached by Yugoslav President Slobodan Milosevic and US Special Envoy Richard Holbrooke in October requires the Serbian security forces to withdraw from the province or return to barracks.

The ethnic Albanian Kosovo Liberation Army (KLA) was also supposed to have suspended its activities.

The job of the OSCE mission is to verify the agreement. The verifiers' duties also include overseeing any elections held in the Serbian province.

The unarmed monitors were granted freedom of movement, given security guarantees and back-up from non-combat Nato surveillance aircraft.

Correspondents say neither the Serbian forces nor the KLA have honoured their commitments.

Cold war past

The OSCE has been primarily concerned up to now with supervising elections in emerging democracies.

Created as the Conference on Security and Co-operation in Europe it grew out of the Helsinki accords signed in 1975 between the two Cold War blocs, undergoing a name change to OSCE in 1994.

It comprises all the European states with the single exception of the Federal Republic of Yugoslavia, the former Soviet republics including Russia, the United States and Canada.

It describes itself as a pan-European security organisation established "as a primary instrument in its region for early warning, conflict prevention, crisis management and post-conflict rehabilitation in Europe".

The OSCE has been active in trying to settle conflicts involving ethnic minorities, and has increasingly taken on a diplomatic role in seeking to prevent conflict.

Since 1995, it has been involved in almost all the countries of the former Yugoslavia (Serbia, Bosnia, Croatia and Montenegro) and in 1997 it monitored elections in Albania.

The OSCE has sent permanent observers to the former Soviet republics of Moldova, Georgia and Tajikistan.

It has sought to promote democratic institutions and help refugees to resettle in Chechnya after the fighting between Chechen separatists and Russian troops.