Germany said today that it is tightening security at airports and train stations after receiving concrete evidence of planned terrorist attacks in the country, including one this month.
"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 press 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.
"According to information from a foreign partner which came to us after the Yemen incident, we suspect a planned attack is due to be put into action at the end of November," De Maiziere said.
Citing security sources, the Tagesspiegel daily said indications had come from the United States that between two and four Al-Qaeda operatives were on their way to Germany and Britain to attempt attacks.
Among the targets Tagesspiegel cited were Germany's popular Christmas markets. The paper added the perpetrators were expected to arrive in Germany on November 22 via India or the United Arab Emirates.
De Maiziere said that the fresh information was obtained in the wake of the discovery last month of two US-bound parcel bombs originating from Yemen, one of which went through Cologne airport in western Germany.
"Since the middle of 2010, the security services have noticed increased indications that the terrorist organisation Al-Qaeda has been planning attacks in the United States, in Europe and in Germany," he said.
"We now have more details and indications of danger ... It is the unanimous assessment of the security services that we are currently dealing with a new situation."
Announcing heightened security measures "until further notice", De Maiziere said: "These are designed to be preventative and act as a deterrent."
Although the evidence of an increased threat is concrete, "it is not cause and should not be cause for us to change our daily lives totally," added the minister.
Chancellor Angela Merkel's spokesman Steffen Seibert told a regular press conference that there were no plans to change her schedule in light of the heightened security situation.
In addition to beefed-up security throughout Germany, there could also be heightened checks on the external borders of the European Schengen visa-free travel zone, the minister said.
Furthermore, recent investigations by the Federal Crime Office have "confirmed the continued efforts of Islamist groups to carry out planned attacks in Germany," he added.
"There are also concrete indications in this case," he said.
Earlier this month, German police arrested a man over videos published on the Internet threatening bomb attacks unless an Islamist jailed earlier this year is released.
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.
"We would be making a big mistake as a society if we allowed our free and democratic way of life to be impaired in any way," said Seibert.
"That would be giving the terrorists a cheap victory."