German authorities are on guard against threats of armed attack on civilians of the kind that killed 166 in the Indian city of Mumbai in 2008, Interior Minister Thomas de Maiziere said Thursday.

Police are taking added precautions, de Maiziere said, a day after Germany tightened security measures citing threats from Islamist militants.

"What we are basically preparing ourselves for, is that terrorists, coming from abroad, commit an attack soon after arrival, without warning, in a building or public place, knowing that they may not survive," de Maiziere told broadcaster ZDF.

"In shop talk, we'd call that something similar to what happened in Mumbai," he added.

Wednesday, Germany said it had strong evidence Islamist militants were planning attacks in the next two weeks, and it ordered security at potential targets such as train stations and airports to be tightened.

Security officials in Berlin said on condition of anonymity then that three scenarios existed -- one involving senior al Qaeda leader Younis al Mauretani, another involving the Mumbai-style attack, and a third pointing tosleeper cells already in Germany.

As de Maiziere spoke, German police were on route to Namibia to aid a separate investigation into a suspect package found at Windhoek airport during security checks for a German tourist flight to Munich.