The employee, who was working with peacekeepers, was snatched from his residence in the city of Fasher.

Security Council envoys had arrived in Fasher to raise concerns about an upsurge in violence in Darfur.

Earlier, Sudanese armed forces, long accused of atrocities in Darfur, launched renewed attacks on rebels.

The government forces said they had taken a key stretch of road from the rebel Sudan Liberation Army, about 100 miles (160km) away from Fasher.

The UN estimates the six-year conflict in Darfur has cost the lives of 300,000 people and driven a further 2.7m from their homes.