Athens, Greece ? Suspected Greek terrorists unleashed an unprecedented two-day wave of mail bomb attacks in Athens and abroad, with one package reaching the office of German Chancellor Angela Merkel on Tuesday.

Anti-terrorism police escort a mail bomb suspect, not named by police, to a public prosecutor’s office in Athens on Tuesday. Eight embassies in Athens were the intended targets of mail bomb attacks Monday and Tuesday.

Greek militant groups are suspected of mounting the attacks targeting embassies in Athens and international organizations and foreign leaders abroad. If that is confirmed, it would mark a dramatic escalation for organizations that have never before attempted to strike targets abroad.

The campaign used small devices that only caused one injury and minimal damage. But it highlights the difficulty of keeping bombs out of the international delivery system — also a target of Yemen-based militants armed with more powerful and potentially deadly explosives.

Security at all embassies in Athens has been increased and authorities suspended all international mail deliveries from Greece for 48 hours for further checks.

By Tuesday evening, at least 11 mail bombs had been detected in the Greek capital — one addressed to French President Nicolas Sarkozy and eight to the embassies of Bulgaria, Russia, Germany, Switzerland, Mexico, Chile, the Netherlands and Belgium.

Two more were destroyed in controlled explosions at Athens’ international airport — one addressed to the European Union’s highest court in Luxembourg and the other to law enforcement agency Europol in the Netherlands.

A suspicious package addressed to Italian Premier Silvio Berlusconi was also found on board a private mail courier company plane that took off from Athens airport late Tuesday. The plane landed at Bologna airport, where the package was being checked, Greek police said.

It was unclear whether the bomb sent to Germany was delivered by land or air. If sent by plane, it would highlight the potential limitations of air cargo security that remain, despite the concern triggered by the mail bombs dispatched recently from Yemen.

“If they have been flown, then it rather begs the question whether European freight air security is up to muster at all,” said UK-based aviation security consultant Chris Yates.

But transportation industry officials also said there are few if any security checks on packages transported within the European Union by road or rail.

“Once they’re in Europe, the goods are free to move around,” said Robert Windsor, manager of trade services at the British International Freight Association.

German Interior Minister Thomas de Maiziere said the package that arrived Tuesday at Merkel’s office was sent from Greece two days earlier by UPS delivery and resembled the Athens packages.

UPS, which transports mail in Europe both by ground and air, said it was aware of reports it had delivered the package but could not confirm them. “We’re working closely with authorities to investigate,” UPS spokesman Norman Black said by e-mail.

Sarkozy said French authorities were working with Greek police.

“The threat is very serious. We are extremely vigilant and I am following it very closely,” Sarkozy said during a visit to London.

Bombs addressed to embassies and state leaders were not likely to reach their intended targets, said Andrew Silke, Director Terrorism Studies at the University of East London. But the bombers probably achieved their aim by generating worldwide publicity.

“If they had just left the devices on the streets of Athens it wouldn’t have got nearly anything like the attention it got internationally,” Silke said. “This happening so close to the Yemeni attempt to get bombs into the United States means it probably has more of a resonance that it would otherwise.”

Mail bombs are also easy to put together, he noted.

“It’s a very simple way to cause an awful lot of disruption,” Silke said. “The devices are usually very simple to make. The ingredients needed to make them are cheap.”

With so much attention, “I wouldn’t be surprised if this would lead to a significant increase in this type of attacks in the coming months.”

No connection has been made to the mail bombs from Yemen that were found on aircraft in Britain and Dubai, and Greek authorities are focusing on domestic groups.

The attacks began Monday when a mail bomb addressed to the Mexican embassy exploded at a delivery service in central Athens, lightly wounding one worker.

Police arrested two men in their twenties shortly after the blast. They were allegedly carrying mail bombs addressed to Sarkozy and the Belgian Embassy, along with handguns and bullets in waist pouches.