Four parcel bombs have now been sent from the Italian city of Bologna, including one to European Commission president Romano Prodi sent on Saturday, followed by booby-trapped packages received on Monday by European Central Bank (ECB) president Jean-Claude Trichet and Europol chief Juergen Storbeck.
Bologna prosecutor Enrico Di Nicola told Italian daily Corriere della Sera "anarchist groups" were responsible for the attempted attacks.
Prosecutors in Germany, where the ECB has its headquarters, began an investigation into an unnamed Italian "anarchist" group for attempted murder over the device sent to Trichet.
The Dutch prosecutor's office announced on Tuesday a suspicious package was found at Eurojust after sources in the Italian city of Bologna told the news agency ANSA a parcel bomb had been sent there.
A team of explosives experts was at the scene to investigate the package, but was called away. According to the ANP news agency the investigation would continue later on Tuesday.
Eurojust was founded to facilitate cooperation in crime fighting within the European Union.
Dutch prosecutors confirmed on Tuesday the parcel bomb sent to the headquarters of European police organisation Europol on Monday came from Bologna.
"We are still investigating whether the package was sent by the same person who sent parcel bombs to... Prodi and... Trichet," the office of the prosecutor said in a statement.
More letter bombs
The package sent to Prodi was the only one that burst into flames - the head of the EU's chief executive escaped unharmed when he opened the parcel.
On Monday, parcel bombs arrived at the European Central Bank in Germany and at the European police organisation Europol in the Netherlands. Both packages were disarmed and are being investigated.
Di Nicola warned there could be more booby-trapped letters on their way.
"I think we are faced with an organisation that is political in character, that does not want to cause great damage but to create a feeling of fear and targeting those whom they consider to be the masters of Europe"
Enrico Di Nicola,
"One could reasonably assume that the attacks are not over yet," he told the paper.
He pointed to "anarchist groups" as the possible senders of the explosive packages.
"This is not a hypothesis we should exclude... I think we are faced with an organisation that is political in character, that does not want to cause great damage but to create a feeling of fear and targeting those whom they consider to be the masters of Europe," he said.
Commission officials said security was being stepped up after the spate of attempted attacks.
EU bodies housed in Belgium - including the European Commission, the European Parliament and the European Council - have been asked to be particularly vigilant to any mail sent from Bologna, the Belgian interior ministry said.