Greece has stopped all airborne parcels headed out of the country after the discovery of three letter bombs addressed to European leaders.
Italian Prime Minster Silvio Berlusconi, German Chancellor Angela Merkel and French President Nicholas Sarkozy were all targeted.
Ms. Merkel called Wednesday for better international coordination on security rules for air cargo.
The letter bombs sent from Greece appeared to be part of a group of explosive-packed packages that also targeted eight embassies in Athens and EU institutions.
Three of those bombs exploded or caught fire, slightly injuring one person. The rest of the packages, including those addressed to the European leaders, were intercepted.
Greek police believe left-wing extremists are behind the attempted bombings and have arrested two suspects.
They say they have found no connection to the similar Yemen-based air-cargo bomb plot linked to al-Qaida and targeting the United States.
Police say no mail will fly out of Greece for the next two days, as authorities screen thousands of parcels that were set to leave the country.
A package bomb sent from Greece to Mr. Berlusconi blew up at an airport in Bologna. No injuries were reported.
German authorities found a parcel bomb in Ms. Merkel's mail room on Tuesday. The chancellor was out of the country at the time.
Greek authorities are questioning two suspects arrested Monday carrying two bombs, one of them addressed to Mr. Sarkozy. One of the detained is linked to the Greek militant group, Conspiracy Cells of Fire.
The embassies in Athens of Bulgaria, Russia, Germany, Switzerland, Mexico, Chile and the Netherlands were targeted. None of those explosives caused serious damage.
Some information for this report was provided by AP, AFP and Reuters.