Arrests over alleged corruption at the European Parliament are “very, very worrisome”, the EU’s foreign policy chief Josep Borrell has said.
And Irish Foreign Affairs minister Simon Coveney said the charges against four people were “very damaging”.
Among the arrested was European Parliament Vice President Eva Kaili – believed to be one of those charged.
Prosecutors suspect a Gulf state – reportedly Qatar – tried to influence parliament by donating money or gifts.
Qatar has denied misconduct.
Belgian police seized cash worth about €600,000 ($632,000; £515,000) in 16 searches in Brussels on Friday. Computers and mobile phones were also taken, to examine their contents.
Four people have been charged while two have been released, prosecutors said on Sunday.
No suspects have been publicly named but Ms Kaili is understood to be among those who have been indicted.
“They are charged with participation in a criminal organisation, money laundering and corruption,” the Belgian federal prosecutor’s office said in a statement.
Ms Kaili – an MEP for eight years – was suspended from her duties as one of 14 vice-presidents by president of the European Parliament Roberta Metsola.
She has also been suspended from the parliament’s Socialists and Democrats Group, and expelled from the Greek centre-left Pasok party.
Prosecutors in Greece have reportedly frozen all of Ms Kaili’s assets.
Watchdogs and opposition MEPs said the bribery investigation could represent one of the biggest corruption scandals in European Parliament history.
“Certainly the news is very, very worrisome,” Mr Borrell told reporters on Monday as he arrived at a meeting of EU foreign ministers.
“We are facing some events, some facts, that certainly worries me as a former president of the European Parliament.”
Mr Borrell said the investigation did not target anyone from the EU’s diplomatic service. (BBC)