Germany on Wednesday tightened security at airports and train stations, citing intelligence reports which show Islamist militants plan to strike the country at the end of November.
“From today, there will be a visible police presence. I thought it should be explained to citizens,” Interior Minister Thomas De Maiziere told a hastily called news conference in Berlin.
“There will also be a variety of measures that will not be visible. There is reason for concern, but no reason for hysteria,” he added.
Evidence of a potential attack towards the end of the month came from a “foreign partner,” he said.
The federal police force has now been ordered to step up security at airports and train stations.
Officials say there could also be heightened checks on the external borders of the European Schengen visa-free travel zone.
Earlier this month, German police arrested a man for videos he posted on the Internet threatening bomb attacks unless authorities freed a jailed Islamist extremist.
In October, De Maiziere warned against “alarmism” about the threat of terrorist attacks, after the United States, Britain and Japan issued a travel alert for Europe.
This earned him criticism in some quarters for downplaying the threat and being insufficiently tough on terror.