Three Bulgarian helicopter crew members contracted to the U.N. World Food Programme were kidnapped in Darfur on Thursday, officials said, the latest in a wave of abductions hindering aid in Sudan's war-torn region.

Three helicopter crew members...managed by WFP have been abducted by armed men...at an air strip today, WFP spokeswoman Amor Almagro said.

The Bulgarian Foreign Ministry said all three were Bulgarian nationals working for an aviation company contracted to the United Nations.

Bulgarian private airline company Heli Air Services, which employed the three men, said talks for their release were underway and that they were in good health.

The last information is that the crew is well. There is no danger to their health at the moment. Negotiations with the kidnappers have started, Heli Air Services executive director Vasil Valkov told Bulgarian national radio.

He said talks were handled by a special headquarters set up by the Sudanese government, U.N. officials and the Bulgarian foreign ministry and that no ransom had been demanded so far.

Darfur's insurgency has descended into chaos with rebel groups divided and militias mobilised by Khartoum breaking ranks. Clashes have escalated between guerrillas and the government and peace talks have floundered.

The lack of security and the kidnappings -- there have been more than a dozen abductions targeting foreign workers by young men demanding ransoms since 2009 -- have hindered what is the world's largest humanitarian operation.

The three were taken from an air strip some 65 km (40 miles) southeast of el-Geneina, capital of West Darfur state, WFP said.

All of those snatched in Darfur have been released safely without any injury to them. The kidnappings have been fuelled by reports of Khartoum paying ransoms, which it denies.

The Sudanese government has yet to apprehend any of those responsible for the kidnappings, despite officials having said they knew who the criminals were.

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