First, it was printers packed with explosives from Yemen being shipped through Germany. Then, just days later, a parcel bomb from Greece ended up in the mailroom at Angela Merkel's Chancellery.

The German government is concerned about the recent spate of terrorist deliveries. At a cabinet meeting on Wednesday, the Interior Minister Thomas de Mazière announced that Berlin is to demand a swift Europe-wide reassessment of air cargo traffic safety regulations. At a meeting of EU interior ministers on Monday, Germany will push for the appointment of a working group which would then present its first findings at the EU summit in December.

German security officials have become increasingly concerned since learning the details of the explosives delivered from Greece to the Chancellery in Berlin on Tuesday. The package, which was disguised as a book delivery wrapped in brown paper and addressed personally to Angela Merkel, was discovered during routine screening in the mailroom. Security officials found an explosive device hidden within a hollowed-out book -- a kind of pipe bomb filled with gunpowder, together with a detonator. A water cannon was then used to render the package harmless.

But even as the government points to the fact that its security measures worked, the case still reveals holes in current security monitoring of air cargo. According to SPIEGEL ONLINE source, the parcel bomb, sent by the freight delivery service UPS, was screened twice in transit from Athens: once at the Cologne-Bonn airport and again at Berlin Schönefeld. Nothing was found suspicious. German investigators said the simple detonation device, which was designed to ignite the gunpowder when the book cover was opened, should have been easy to detect. The fact that it wasn't, say investigators, is a "substantial problem."

Gaps in Security

Security experts say the case highlights gaps in security checks. It's unclear just how well trained the inspectors that man X-ray machines at cargo handling companies actually are. It's also difficult to later determine when and where packages have been screened.

Investigators are now certain the package delivered to the Chancellery was sent by the Greek far-left group "Conspiracy Nuclei of Fire." Investigators have received detailed information from Greece on the letter bombs, most of which where sent to foreign embassies, including the German Embassy in Athens. All of them had an identical technical design and exterior appearance to the parcel that arrived in Germany. In every case the terrorists had typed the recipient's address onto a white label with the sender's address, in most cases a part of the Greek government, on an identical label. On Monday, two suspects were arrested with five more having been identified on Wednesday. Athens suspended all freight and mail flights for two days and thousands of packages were examined on Wednesday.

The group, which has been active for several years, had previously only operated within Greece. But its range now seems to have expanded. Another package thought to have originated with the group, addressed to Italian Prime Minister Silvio Berlusconi, was destroyed in Palermo on Tuesday evening.

On Wednesday, German public prosecutors launched a preliminary investigation into the bomb at the Chancellor's office. Investigators are working through the Federal Criminal Police Office (BKA) to get access to Greek information on the results of local enquiries -- in the hope of finding those responsible for the Chancellery delivery. Investigators remain puzzled over why exactly the group sent explosive packages to Germany and Italy.

Investigators Journey to Athens

Despite currently having no indications of further parcel bombs, the BKA has sent staff to Greece to conduct further investigations. BKA President Jörg Ziercke said investigators are to learn about the results of the interrogation of the two detainees and observe the examinations of the packages found there. The two suspects arrested on Monday were found carrying additional package bombs and two Glock pistols.

Experts say that, had the package addressed to Merkel detonated, it would have produced a jet of flame that could have seriously injured Chancellery employees. During a tour this week of the mailroom and security department at the Chancellery, Merkel thanked employees for their dedication. While nobody believes the parcel bomb could have made it to the chancellor herself, an explosion in the postal department would have been a "catastrophe," according to one official.

Security staff are currently looking into possible security shortcomings at the Chancellery and ministry buildings. Officials are concerned that further parcel bombs could be on their way from Greece to Germany. State facilities are also on high alert. So far, though, no additional packages have been found.

Finding a Balance

According to government representatives, Germany wants to take a leading role at the EU-level in the initiative to tighten air freight security regulations. A government spokesman pointed out that Germany is particularly important to the process because the country is responsible for handling the majority of air cargo between the Middle East and the US. According to industry sources, in 2009 alone 3.9 million tons of air cargo was transported via Germany. Several major logistics companies operate large distribution centers at the country's airports.