Suspicious luggage 'was test of airport security'

But officials are still trying to determine who carried out the test.

Thomas de Maiziere said that German experts sent to Windhoek airport after the incident on Wednesday had inspected the bag and determined it was made by an American firm to test airport security measures. He did not say who may have left the case in the luggage hall, adding that German agents were still investigating.

The suitcase was found in the luggage hall area near where bags intended for the Air Berlin flight were. Following the discovery, the Air Berlin luggage was rechecked and passengers were required to identify their bags, none of which were missing, and after a lengthy delay the plane was able to leave and arrived with all passengers in Munich.

The threat came amid heightened concerns of terrorist threats against Germany that prompted Mr de Maiziere to raise the country's threat level even before the Windhoek incident.

"Most important is that there were no explosives in the bag and there was never any danger to the passengers at any time," the Interior Minister said.

When asked if it could have been a German security test, Mr de Maiziere said that was "unlikely but part of the investigation".

Concern about the possibility of international flights being targeted by terrorists rose last month when bombs were found on cargo planes from Yemen to the US.

One of them went through a German airport before being found in Britain.

The Windhoek incident came as Germany already was on edge after Mr de Maiziere raised the country's terrorist threat level, saying intelligence services had received a tip from an unspecified country about a suspected attack planned for the end of November.

In comments published in Germany's Bild newspaper, Germany's federal police president said the terrorist threat facing the nation was "more serious than ever before".