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

Interior Minister Thomas de Maiziere said details of the plot emerged after parcel bombs were dispatched from Yemen to U.S. targets at the end of October, and separate postal bombs by suspected Greek militants were sent to prominent figures including Chancellor Angela Merkel.

At a news conference hastily convened at his ministry in Berlin, de Maiziere said the security threat in Germany had risen and that intelligence services had received concrete indications that attacks were planned at the end of November. Germany was the source of much of the planning for the 9/11 attacks on the U.S.

De Maiziere said he had instructed German police to step up security measures around the country.

“Citizens will be able to see such police measures,” he said. “In addition to this, there are a lot of measures that they won’t be able to see.”