The ECB's Jean-Claude Trichet is among those targeted

Four devices have been posted from Bologna in the past week by suspected anarchists.

Post offices will now halt all packets addressed to EU bodies, said Bologna assistant prosecutor Luigi Persico.

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 European Central Bank chief Jean-Claude Trichet, and crime-fighting and justice agencies Europol and Eurojust.

None of the devices has caused injury.

An unknown Italian group calling itself the Informal Anarchist Federation is believed to be behind the campaign.

It has recently threatened to target "the apparatus of control that is repressive and leading the democratic show that is the new European order".

The order for mail to be blocked covers all post offices in the Emilia-Romagna region, in which Bologna is situated.

Police will be able to open or X-ray all packages.