EU officials also warned Bulgaria, which just joined the organization 18 months ago, it stands to lose $11.2 billion over the next six years if it doesn't improve its anti-crime efforts, The Guardian reported.

The EU also said Romania's judicial reforms have been limited but stopped short of withholding aid, the British newspaper said.

Observers said the reports sent a message to other nations seeking membership in the commission, including Croatia, Serbia and Turkey.

"With anti-corruption reform faltering since EU accession, the cases of Bulgaria and Romania show that EU membership is no magic bullet," Transparency International, the anti-corruption campaign, said in a statement.