The EU on Wednesday defended a trip by its top diplomat to Morocco, which has been linked, along with Qatar, to a graft scandal unrolling at the European Parliament, AFP reported.

As "there is no proof" of wrongdoing at this stage, it is right the trip by EU foreign policy chief Josep Borrell on Thursday and Friday should go ahead, a spokesman for Borrell said.

"No one has officially said from the judicial point of view that Morocco as a country is guilty, and Morocco should be avoided in international contact," said the spokesman, Peter Stano.

The scandal erupted last month when Belgian police raided several addresses used by some lawmakers and aides in the European Parliament, lobbyists, and NGO heads.

The searches turned up 1.5 million euros ($1.6 million) in cash, suspected to be pay-offs as part of efforts to influence decisions in the European Parliament.

Four suspects are in custody, including a Greek MEP, Eva Kaili.

Kaili, who was stripped of her position as one of the parliament's 14 vice presidents after her arrest, insists she is innocent.

Through her lawyer she has expressed ignorance about 150,000 euros in cash found in her Belgian residence.

Her Italian boyfriend, Francesco Giorgi, a parliamentary aide, has reportedly made a confession to Belgian prosecutors, which also alleges Moroccan involvement.

MEPs have raised concerns over Morocco's possible involvement following developments in the case set out in Belgian newspapers.

The affair has cast a cloud over other EU institutions, and increased media scrutiny of dealings by EU commissioners and top officials who recently dealt with Qatar and Morocco.

Stano said the matter "is in the hands of the judiciary in Belgium" and "we have full trust" in their work to investigate the allegations.

The four suspects in Belgian pretrial detention are: Kaili, Giorgi; a former Italian MEP, Pier Antonio Panzeri; and Niccolo Figa-Talamanca, the Italian head of an NGO suspected of making payments to MEPs.

All four are charged with "criminal organization, corruption and money laundering."

Greece and Italy have launched their own investigations into the alleged corruption.