Four people have been arrested and placed under pre-trial detention including a senior EU Member of Parliament in a corruption scandal which has rocked the European Parliament.

Belgian police conducted a series of raids on offices and homes, one of which led to the discovery of a suitcase containing €600,000 ($632,868). The scandal is being linked to an unnamed Gulf state. Local media pointed the finger at Qatar though the authorities there have denied any wrongdoing.

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A Greek vice president of the EU Eva Kaili was expelled from her own party and has been suspended from all her duties within the European Parliament pending the outcome of the police investigation.

The corruption scandal follows months of inquiries by the Belgian authorities into a suspected criminal organization which is believed to have infiltrated the very heart of the parliament.

Not an isolated incident

The EU Foreign Policy Chief Josep Borell said the charges were "very, very worrisome." 

Meanwhile, EU watchdogs and some opposition MEPs said the bribery allegations could be one of the biggest corruption scandals ever to hit the European parliament.

Michiel van Huiten, Director of Transparency International EU called it "an egregious case of alleged corruption" but added that it was by no means an isolated incident.

"Over many decades, the parliament has allowed a culture of impunity to develop, with a combination of lax financial rules and controls and a complete lack of independence - or indeed any - ethics oversight," he said.

The European Parliament is the organization's only directly elected institution with 705 MEPs elected by the voters in all 27 of the member states.  Its main tasks are to scrutinize proposed legislation, agree the EU budget and vote on European laws.