MILAN (Reuters) – A package addressed to Italian Prime Minister Silvio Berlusconi found on a cargo plane from Athens caught fire when police opened it, an Italian police source said on Wednesday.

Italian police were checking the package at Bologna airport where the Paris-bound TNT cargo plane from Athens was made to land after authorities were alerted that it was carrying a suspect parcel addressed to Berlusconi.

Small bombs exploded at the Swiss and Russian embassies in Athens on Tuesday and a possible bomb was intercepted at German Chancellor Angela Merkel's office, the latest in a wave of attacks by suspected Greek leftist guerrillas.

"Police found the package addressed to Berlusconi and it caught fire while it was being checked," the senior police source said. "The explosive substance is still unknown and it is being verified. Police suspect that it could be a package similar to that addressed to (German Chancellor) Angela Merkel."

The sender of the package was unknown, and it was mailed via a Greek company, the source said.

Greece suspended all overseas air shipments of mail and parcels for 48 hours on Wednesday following the attacks.

A Greek police source had said the courier plane was flying from Athens to Rome late on Tuesday when it was forced to land in Bologna.