If that doesn't happen and it's all just tactics, the international community will agree on further measures. Then sanctions cannot be ruled out, he told N-24 television.
Only a serious return to negotiations would prevent the international community from taking further measures and imposing sanctions, Westerwelle told reporters in Berlin.
On Tuesday, Iranian President Mahmoud Ahmadinejad said Iran was ready to send its enriched uranium abroad in what appeared to be an easing of its position in the nuclear dispute. He appeared for the first time to drop Tehran's long-standing conditions on a deal with global powers.
The United States said that if Iran was serious, it should tell the International Atomic Energy Agency (IAEA).
German Chancellor Angela Merkel echoed Westerwelle, saying at a news conference that Germany would wait and see whether Iran suited actions to its words.
We have to see whether Iran actually takes up the offer to enrich uranium abroad, she said. One speech does not necessarily mean it will take further steps.
The German government, like the United States, has already said Iran should tell IAEA, the United Nations nuclear watchdog, if it was will to send its enriched uranium abroad.
Western powers fear Iran is trying to build nuclear bombs and that the long-range ballistic technology used to put satellites into orbit can also be used to launch warheads. Iran says its nuclear programme is solely to generate electricity.
(Reporting by Sarah Marsh, Dave Graham, Thorsten Severin; editing by Tim Pearce)