Steinmeier said in a statement "the Iranian president's announcement deeply worries me", stressing "only a cooperative attitude can open the way for negotiations".

He also asked Iran to "take seriously the international community's concern and to finally suspend enrichment".

Iran announced on Tuesday it had started the installation of 6,000 new centrifuges "five times more capable" than existing one, to enrich uranium at its main nuclear plant in Natanz in the country's central region.

The West fears Iran could use enriched uranium to make nuclear weapons though Tehran denies these claims.

The UN Security Council has punished Iran's refusal to suspend the process with three sets of sanctions.

Permanent Council members Britain, China, France, Russia and the United States plus Germany will meet with Iran on April 16 to discuss the matter further.

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