Westerwelle also indicated that other sanctions on Iran are being considered by EU foreign ministers as they meet Monday in Luxembourg.
On his way into the meeting British Foreign Secretary William Hague said new sanctions would be "a sign of our resolve in the European Union that we will step up the pressure."
Hague said such pressure would continue to mount "over the coming months unless negotiations succeed. We remain open of course to success of negotiations."
The foreign ministers of France and Germany made similar calls. They did not elaborate on the kind of measures under consideration.
The United States and its allies accuse Iran of covertly developing nuclear weapons. Tehran denies that.