Al Qaeda is planning attacks on high-speed trains in Europe, and authorities in Germany are stepping up security on the country’s rail system, Reuters reports.

The information about planned attacks came from the U.S. National Security Agency (NSA), which apparently intercepted a call between senior al Qaeda members several weeks ago, but the German Interior Ministry says it regularly received information about such threats and was not planning to increase overall security, the article reports.

German authorities have tightened security on high-speed Intercity-Express (ICE) routes and at stations with “invisible measures,” including the deployment of plain-clothes police officers.