The EU’s credibility is at stake, EU foreign ministers warned on Monday, following allegations Qatar lavished cash and gifts on European Parliament officials to influence decision-making. Greece on Monday froze the assets of a key suspect in the case, Eva Kaili, a vice-president in the European Parliament and one of four people arrested and charged in Belgium over the weekend, a source with knowledge of the matter said.

Kaili’s office did not respond to a request for comment. Qatar has denied any wrongdoing. Belgian prosecutors searched 16 houses and seized €600,000 in Brussels on Friday as part of the probe. Four people were subsequently charged with “participation in a criminal organisation, money laundering and corruption”, prosecutors said in a statement on Sunday.

They did not name the suspects, but the European Parliament said at the weekend it had suspended Kaili from her duties, while the Greek socialist PASOK party announced it was expelling her from its ranks. “This is an unbelievable incident which has to be cleared up completely with the full force of law,” German foreign minister Annalena Baerbock said as she arrived for a regular meeting with her EU counterparts in Brussels. “This is about the credibility of Europe.” Irish foreign affairs minister Simon Coveney echoed her concern.

“It is damaging. We need to get to the bottom of it.” Belgian prosecutors said they had suspected for months that a Gulf state was trying to buy influence in Brussels. A source with knowledge of the case said the state was Qatar. A Qatari official denied at the weekend accusations of possible misconduct. “Any association of the Qatari government with the reported claims is baseless and gravely misinformed,” the official said.

The investigation comes as World Cup host Qatar is in the global spotlight, amid criticism of its human rights record, including its treatment of migrant workers. In a speech in the European Parliament on November 21, Kaili lashed out at Qatar’s detractors and hailed the energy-rich Gulf State as “a frontrunner in labour rights”.