Parcels sent from Italy's Bologna region to European Union institutions are being blocked after a spate of letter bombs.
Four devices have been posted from Bologna in the past week by suspected anarchists.
One of the four devices exploded when European Commission President Romano Prodi opened it at his home in Bologna.
The three other bombs were sent to the chief of the European Central Bank, Jean-Claude Trichet, and to the crime-fighting agencies Europol and Eurojust. None of the devices has caused injury.
A number of European Union police forces have combined to find those suspected of waging the campaign.
An Italian group calling itself the Informal Anarchist Federation had threatened a campaign against what it called the 'new European order' just days before the first device was sent on Saturday.
Meanwhile in Hamburg, German police and soldiers sealed off a military hospital after receiving information that Islamic militants planned a car bomb attack on the building.
