"The events of the past few months have caused significant damage to the ITUC's reputation," said Akiko Gono, the president of the body, which federates 338 unions in 168 countries and territories around the world.

"We are determined to protect the ITUC from any form of improper influence, or indeed the appearance of such influence."

The ITUC also said a report from its special commission and external auditors had found "no evidence of donations from either Qatar or Morocco influencing the ITUC's policies or programmes".

Visentini has admitted receiving 50,000 euros from the NGO of former MEP turned lobbyist Pier Panzeri, who allegedly ran the bribery ring and cut a deal with prosecutors last month in return for a lighter sentence.

Brussels has been rocked by the huge graft inquiry, which sent shock waves through the EU elected assembly and triggered international controversy.

Both Qatar and Morocco insist they played no role in the scandal, but prosecutors say Panzeri has confessed to distributing cash bribes on their behalf to influence Brussels politicians.

Visentini said the cash was to cover costs from his campaign to become ITUC general secretary of the ITUC.

The organisation said it will hold an "extraordinary world congress" to elect a new secretary.

In December Belgian police seized more than 1.5 million euros in cash during raids around Brussels and arrested six suspects, including Panzeri and then-parliamentary vice president Eva Kaili.