Greece suspended all overseas air shipments of mail and parcels for 48 hours on Wednesday following a wave of attacks by suspected leftist guerrillas on government targets in several west European countries.
Small bombs exploded at the Swiss and Russian embassies in Athens on Tuesday, a package with explosives was intercepted at the German chancellor's office and another package addressed to the Italian prime minister caught fire when it was checked by authorities, an Italian police source said.
Two more suspect packages detonated by police at the cargo terminal of Athens airport on Tuesday evening contained explosives and were addressed to Europol and the European Court of Justice, police officials said.
"Following a recommendation by Greek police, Greek aviation authorities decided to suspend the shipment of mail and packages abroad for 48 hours, aiming to make checks," Greek police said in a statement.
Police had already arrested two Greeks, aged 22 and 24, on Monday in possession of two bombs including one addressed to French President Nicolas Sarkozy. The latest incidents took the total of actual or suspected bombs to 14 since Monday.
Police said on Monday that one of the two arrested men may be a member of the Fire Conspiracy Cells, who have staged several attacks on government targets over the past year.
Greeks have become used to gas canister and bomb attacks against public buildings and police stations in the last two years, as well as anti-capitalist urban guerrilla attacks down the decades.
The wave of bombs may be intended to galvanise an anti-government vote in Sunday's local elections.
Prime Minister George Papandreou's Socialists already fear a backlash against the radical tax hikes, pension freezes and cuts in spending and public sector wages they have imposed.
The attackers also may want to demonstrate that they are still active after the arrests of more than a dozen suspected members of guerrilla groups this year.
Papandreou vowed to "be merciless to those who attempt in vain to rock social peace with terrorist acts and hurt our country's image internationally during a very difficult period".
The two arrested men were both charged with participating in a terrorist group and with illegal possession of explosives and weapons, a court official said.
No one was injured at the Swiss or Russian embassies, and Greek police said the bombs that had been found were mostly too small to kill anyone. "When the external packaging was removed, the contents burst into flames," a Swiss Foreign Ministry spokesman said.
Other parcel bombs found on Tuesday included one outside parliament addressed to the Chilean embassy, one each at the Chilean and Bulgarian embassies, and one addressed to the German embassy, at the offices of a courier company.
In Germany, police intercepted a package containing explosives sent from Greece to Chancellor Angela Merkel's office in Berlin. Addressed to Merkel personally, the suspect parcel was found in the mailroom of her chancellery while she was in Belgium, and was rendered harmless, the government said.
In Italy, a cargo plane from Athens was made to land at Bologna airport after authorities were alerted that it was carrying a suspect parcel addressed to Italian Prime Minister Silvio Berlusconi. The package caught fire as it was checked, an Italian police source said.
Papandreou, in office for only 13 months and nervous about a popular backlash in the local polls, has threatened to call a snap parliamentary election if voters do not back his austerity policies in local polls this weekend.
Blanka Kolenikova, an analyst at IHS Global Insight, said the austerity programme, agreed with the European Union and International Monetary Fund as a way of rescuing Greece from a debt mountain and near-insolvency, was likely to be the main trigger for the wave of bombs.
"Given that left-wing militants tend to blame the country's fiscal woes on 'the wheels of capitalism', the unpopular cost-cutting measures could see recruits to such groups increasing," she said.
Greece's stock market took the attacks in its stride, and shares closed little changed on Tuesday.