A suspect package intercepted at a Namibian airport was a dummy used to test security, German officials say.
Interior Minister Thomas de Maiziere said officials had established that it was a so-called "real-test suitcase".
He said no explosives were discovered in the case, which was found near luggage about to be loaded on to a Munich-bound flight.
It is not known who left the case at Windhoek airport on Wednesday, triggering an international alarm.
But Namibian police said they would deal "severely" with anyone involved.
"The Namibian police force wants to send out a stern warning to people with ill intentions that it will not allow Namibia to be used as a testing ground by anyone," The force's inspector general, Sebastian Haitota Ndeitunga, said in a statement.
He added that neither the US, German nor Nambian governments were aware of the package.
The incident came just hours after Germany had raised its terrorist threat level, saying it had received a tip-off from an unspecified country about a suspected attack planned for the end of November.
Mr de Maiziere told a news conference in the northern city of Hamburg on Friday that experts from the German federal police had flown to Windhoek to examine the suitcase.
"The outcome is that the luggage turned out to be a so-called real-test suitcase made by a company in the United States.
"This company is a manufacturer of alarm and detection systems and these real-test suitcases are built to test security measures," he said.
Mr de Maiziere did not say who had left the suitcase, but said German agents were still involved in the investigation.
Asked if it could have been a German security test, he said that was "unlikely but part of the investigation".
He added: "The most important thing is that there were no explosives in the bag and there was never any danger to the passengers at any time."
The BBC correspondent in Berlin, Steve Evans, says the minister's statement raises a number of questions, such as, if it was a test done by local officials, why wasn't the true nature of the device revealed immediately?
And, if it was done by a foreign security agency, why didn't they inform the Namibian authorities?
The suitcase was placed alongside baggage about to be loaded on to an Air Berlin plane at the airport near the Namibian capital.
It was seized by Namibian police and an X-ray inspection revealed batteries that were attached with wires to a "detonator" and a ticking clock.
The Air Berlin plane, with around 300 passengers and crew on board, was delayed for six hours before being cleared for take-off to Munich, where it arrived on Thursday morning.