By Renee Maltezou and Angeliki Koutantou

ATHENS (Reuters) - Greek police detonated a parcel bomb on Thursday addressed to the French embassy in Athens and were investigating others packages at a courier company in a city suburb.

A police source said it was too early to say whether they were part of a new wave of devices sent to foreign governments and embassies since Monday by what the government has described as Greek "extreme left, anarchist groups."

But a Transport Ministry source said authorities had no plans to extend a 48-hour suspension on air freight abroad of mail and packages from Greece imposed on Wednesday.

"Greece is not planning for the time being to extend the suspension. The reason for the 48-hour pause was to check all parcels destined for delivery abroad," the official, who declined to be named, said.

"The checks will be concluded later tonight," the official said. The suspension is set to end shortly after midnight Greek time (6 p.m. EDT). Another official said, however, that a final decision would be taken after consultation with police.

Small bombs exploded at the Swiss and Russian embassies in Athens on Tuesday, a parcel with explosives was intercepted at the German chancellor's office and another package addressed to Italy's prime minister caught fire when it was checked.

The devices may be intended to spur an anti-government vote in Sunday's local elections in protest against Prime Minister George Papandreou's austerity plan, agreed with the EU and International Monetary Fund to deal with Greece's debt mountain.

After more than twenty arrests among their ranks, urban guerrillas may also want to show that they can still strike.

"All evidence shows this is a clear domestic case, with no connection with international terrorism," Greek Foreign Minister Dimitris Droutsas has said. "The evidence so far shows we are dealing with extreme left, anarchist groups."

Police carried out Thursday's controlled explosion outside a courier company, a Reuters witness said. A police source said the bomb had been concealed in a large book.

"It was an explosive device," a police spokesman said.

Police said the package addressed to Italy's Silvio Berlusconi was also a book containing an explosive device. Police say most of the parcel bombs burst into flames when they are opened rather than exploding in transit.

Police were also investigating suspicious parcels at a courier company in the Athens suburb of Markopoulo.

"We are checking them," a police spokesman told Reuters, without saying how many suspect packages there were.

(Additional reporting by Ingrid Melander; Editing by Alison Williams)