A corruption scandal has been rocking the European Parliament since Belgian authorities raided parliament offices two weeks before Christmas.
Four people - all affiliated with the chamber - have been charged over allegations Qatar lavished them with cash and gifts to influence decision-making.
The European Parliament said on Monday it had begun a procedure to waive the immunity of two other MEPs after a request from Belgian judiciary.
Qatar has denied wrongdoing.
In arrest warrants issued in Italy, there are also allegations of payments from Morocco. Morocco has not officially commented on the allegations but on Thursday its foreign minister has complained of European parliament 'harassment'.
Investigators searched 19 homes and offices of the European Parliament in raids on Dec. 9-12, recovering 1.5 million euros ($1.59 million) in cash.
WHO'S WHO
The four suspects are charged with participating in the activities of a criminal organisation, money laundering and corruption, and are all in pre-trial detention. Belgian prosecutors only gave their initials but sources close to the investigation confirm they are:
* Eva Kaili: a Greek socialist politician who was one of the European Parliament's 14 vice presidents until mid-December when she was removed from that post over the allegations.
Her Greek socialist PASOK party has expelled her from and Greece has frozen her Greek property.
She has denied any wrongdoing through her lawyers.
* Pier Antonio Panzeri: a former European Parliament member from Italy's centre-left and founder of non-profit group Fight Impunity. Panzeri's lawyer did not reply to requests to comment. Fight Impunity has not responded to a request for comment.
Belgium also submitted European arrest warrants for his wife and daughter in Italy on suspicion of taking part in Panzeri's alleged activities .
Both have denied any involvement.
* Francesco Giorgi: Kaili's partner who is a parliamentary assistant. His LinkedIn account says he is a founder of Fight Impunity and that his specialist areas as a policy adviser are foreign affairs, human rights and the Middle East.
According to two sources with direct knowledge of the matter, Giorgi admitted to Belgian investigators that he took bribes to influence European Parliament decisions and sought to exonerate Kaili.
Giorgi's lawyer said he is currently not commenting on his case.
* Niccolo Figa-Talamanca: an Italian lobbyist and secretary-general of human rights and rule of law campaign group No Peace Without Justice. Prosecutors say the group was used by the suspects to funnel money paid by a Middle Eastern country to buy influence in EU institutions.
Figa-Talamanca could not be reached for comment.
No Peace Without Justice has said he had suspended himself from his role to safeguard the organisation and that the group trusted the investigation would show he had acted correctly.
The European Parliament said on Jan. 2 it had begun a procedure to waive the immunity of two other MEPs after a request from Belgian judiciary.
Sources close to the investigation said both were named by Giorgi and that the MEPs were:
* Marc Tarabella: a Belgian socialist MEP and vice-chair of the parliament’s delegation for relations with the Arab Peninsula.
Tarabella's lawyer Maxim Toller said his client, who denied wrongdoing, was in favour of being stripped of his immunity.
*Andrea Cozzolino: an Italian MEP who worked directly with Francesco Giorgi, the latter being one of his parliamentary assistants.
Cozzolino did not respond to efforts to contact him for comment.
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(Reporting by Charlotte Van Campenhout and Philip Blenkinsop, additional reporting by Renee Maltezou in Athens; Editing by Raissa Kasolowsky)