The University of Wales has suspended its involvement in an archaeological dig in Bulgaria after a senior lecturer was accused of military espionage and expelled.

Douglass Bailey, an American who lectures at Cardiff, had his passport withdrawn and was interrogated for several days before being banned for five years.

Dr Bailey fears he has been the victim of bullying from the Bulgarian regime which has so far refused to return thousands of pounds worth of equipment and documents it seized from his group.

The United States embassy in Sofia has rejected the Bulgarians' claims: "This sort of charge reflects a xenophobia which belongs to Bulgaria's past, hopefully not its future."

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He was leading the Cardiff group in a 25-strong party, including archaeologists from the University of California at Berkeley, which had permission to excavate a 5,000-year-old settlement at Podgorista. However, the dig attracted some hostile attention in the press which Dr Bailey believes may have been fuelled by professional jealousy.

At first he was accused of damaging the site but was then questioned about spying, which carries a jail sentence of at least 30 years in Bulgaria. The claims appear to have been fuelled by the group's aerial photographs of the site.

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"I have been expelled from the country for something I have not done," said Dr Bailey, who has been visiting Bulgaria since 1986. "The Communists are back in power under the label of socialists. There are problems doing academic research in these countries, which have supposedly turned the corner but have actually turned back."

The 14 Cardiff students were searched and questioned by the authorities when they left Bulgaria last month. When Dr Bailey tried to leave his passport was seized and on four consecutive days he was interrogated by the Bulgarian police about four of his colleagues.

Eventually he was driven to the airport, then read a statement that he carried out illegal excavations and put on a flight to Britain, accompanied by armed guards.