According to media reports, Francesco Giorgi, one of the four people currently in custody, has accused Morocco of trying to influence EU policy-making.
Morocco has denounced what it calls "repeated media attacks" and "legal harassment" as the kingdom battles growing allegations that suggest an involvement in the corruption scandal engulfing the European Parliament, dubbed as QatarGate.
"The partnership between Morocco and the European Union is a partnership that faces attacks," Nasser Bourita, Morocco's foreign affairs minister, said on Thursday. "Morocco's position has always been that it is a partnership that must be protected on both sides."
So far, four people have been arrested as a result of the Belgian probe: Greek MEP Eva Kaili, her partner Francesco Giorgi, former Italian MEP Pier Antonio Panzeri, and NGO director Niccolò Figà-Talamanca.
They are accused of participation in a criminal organisation, corruption and money laundering. More than €1.5 million in cash have been seized across dozens of home and office searches.
The plot further thickened this week after Belgian authorities requested the lifting of the immunity of two additional MEPs from the socialist group, Marc Tarabella (Belgium) Andrea Cozzolino (Italy), and whose lawyers have told media they will not impede the process and wish to be heard.
Although the investigation was initially launched in connection to illicit lobbying conducted by a Persian Gulf country, widely identified as Qatar, attention has recently shifted to Morocco and its potential participation in the cash-for-favours scheme.
According to information obtained by Belgian newspaper Le Soir and Italian newspaper La Repubblica, Francesco Giorgi has confessed to being part of an "organisation" used by both Qatar and Morocco with the aim to influence EU policy-making.
Giorgi tried to exonerate Eva Kaili by accusing Cozzolino, his former boss, and Tarabella of accepting cash through Panzeri's management. Kaili's lawyer has said his client is innocent and feels "betrayed" by Giorgi.
The Belgian prosecutor had previously referred to "large sums of money" and "substantial gifts" as a key element of the graft scandal.
Qatar has denied any wrongdoing and described the claims as "baseless" and "gravely misinformed."
The newspapers also reported that Giorgi, Panzeri and Cozzolino were in direct contact with agents from Morocco's foreign intelligence agency, known as DGED (Direction Générale des Études et de la Documentation), as well as with Morocco's Ambassador to Poland, Abderrahim Atmoun.
In his capacity as a lawmaker, Cozzolino chaired the European Parliament's delegation for relations with the Maghreb countries, including the EU-Morocco joint parliamentary committee.
'No impunity for corruption'
As new twists and turns mount, the African kingdom tried to counter the accusations.
"The (EU-Morocco) partnership is facing continuous legal harassment. This partnership faces repeated media attacks," Nasser Bourita said on Thursday afternoon.
Bourita was speaking in French during a joint press conference with Josep Borrell, the EU's foreign policy chief, following a bilateral meeting in Rabat.
"This partnership is also facing attacks in European institutions, particularly in the Parliament, through questions directed at Morocco, which are the result of calculations and a desire to harm this partnership," he added.
"Morocco will defend its interests. Morocco is counting on its partners to defend this partnership. It's a partnership of geographical neighbourhood, shared values and converging interests."
For his part, Borrell said the meeting in Rabat had "obviously" touched upon the corruption scandal, among a broad range of policy issues, and wished for the "full cooperation" of all the people involved.
"We are concerned about these events which have been reported in the press. They are disturbing and the charges are serious," Borrell said, also in French.
"The position of the European Union is clear: there can be no impunity for corruption."
No question from the media was permitted during their joint address.
Prior to travelling to Rabat, Josep Borrell had faced criticism over his trip to Morocco, given the fraught political context and the growing number of media revelations.
"Morocco is a very important partner country. It's a southern neighbour," a spokesperson for Borrell said on Wednesday, in response to a question by Euronews.
"Let's not forget: these are allegations at this point, there is no proof, there is no concluded investigation. No one has officially said, from the judicial point of view, that Morocco, as a country, is guilty and that Morocco should be avoided in international contacts."
The spokesperson said it was "appropriate" for Borrell to meet with his counterparts "all around the world" and that the visit to Rabat had been planned "for some time."
"We cannot pre-empt or pre-judge something based on allegations," the official said, noting the EU will wait to have an official confirmation from the Belgian judiciary before making any diplomatic decision.