Thomas de Maiziere said security would be tightened following new evidence of attack plots [Reuters]

Germany is tightening security at airports and train stations after receiving evidence of planned attacks in the next two weeks, the interior ministry has said.

"The security situation in Germany has become more serious," Thomas de Maiziere, Germany's interior minister said on Wednesday.

"We have concrete indications of a series of attacks planned for the end of November," he said, adding there was "reason for concern but no reason for hysteria".

De Maiziere said the latest information came from an "international partner" following the interception of two mail bombs found on cargo planes travelling from Yemen to the United States earlier this month.

One of the packages transited through Cologne airport in western Germany before it was found in Britain.

The minister said the plot points to "the adaptability and the persistence of terrorists in pursuing their aims," and also underlines "the reliability of some leads".

De Maiziere, a senior figure in the country's centre-right government, initially played down the threat last month when the United States and Britain issued warnings that Germany and France could be targeted by al Qaeda and allied fighters.

But earlier this month he acknowledged there were "serious indications" of a threat to Europe and the United States.

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.

Germany has seen itself as a potential target for attacks because it has 4,590 military personnel stationed in Afghanistan, the third largest contingent of the 150,000-strong international force in the country.

Earlier this month, German police arrested a man over videos published on the Internet threatening bomb attacks unless an Islamic fighter jailed earlier this year is released, authorities said.

The country has escaped major terrorist attacks like the ones seen in 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.