Germany's top security official on Tuesday said he will reduce the number of police officers patrolling railway stations and other public places since a terrorism warning last year, but made clear that a threat to the country still remains.

Germany is a target for Islamic extremists, but the incidents that prompted the heightened security have been addressed, Interior Minister Thomas de Maiziere said. Those included an unsuccessful attempt by al-Qaida's Yemeni offshoot to blow up two cargo planes over the U.S., and a report that Islamic extremists were planning an attack within Germany by the end of November, he said.

"We will gradually reduce the visible security measures, but I can't see an 'all clear' in the foreseeable future," he said. Authorities were still evaluating new information on other possible plots, he said, without providing details.

Germany raised its security posture in November after receiving information from its own and foreign intelligence services that led authorities to believe a sleeper cell of some 20 to 25 people may have been planning an attack inside the country or another European nation, a top security official said on condition of anonymity because of the sensitivity of the matter.

Around the same time Germany also received information from U.S. sources that a "Mumbai-style" attack may be planned for Germany, the official said. Later, Germany also received information on possible attacks at Christmas or New Year's.

He would not elaborate on whether the warnings of possible attacks were thought to be connected to each other, nor how reliable the information turned out to be.

Germany has no color-coded or numbered system for measuring security levels, as Britain and France do. It tends to be far more cautious in publicly discussing the degrees of threat, saying it could endanger efforts to prevent an attack.

The European Union now has better methods of ensuring the security of aircraft cargo than it did at the time of the plane plot, and the possible attacks within Germany had not come to pass, de Maiziere said.

"I can't say with certainty if our measures stopped an attack, but they had a good impact," he said, adding that the stepped-up security had served both to calm the public and to show possible terrorists Germany's resolve.

"Of course, it could be possible that they (terrorists) just waited for a few months, but if you think this way then you would be eternally engaged in psychological warfare with them," de Maiziere said.

Following the November terrorism alert, in addition to the hundreds of extra police officers patrolling public areas, authorities in the capital Berlin took the extra precaution of closing off access to the glass dome over the Reichstag parliament building — one of the city's top tourist attractions.

De Maiziere said it was up to parliament to decide whether the Reichstag would be reopened to the public.

The interior minister said that despite the terror threat, Germans continued to visit their country's many Christmas markets and other tourists sites.

Germany has thousands of soldiers serving in northern Afghanistan as part of the NATO security force there and has long expressed concern it could be targeted by extremists.

Though Germany has escaped any major terrorist attacks like the Madrid train bombings of 2004 and the London transit attacks of 2005, at least two major plots have been thwarted or failed before they could be carried out.