"I fear that we will have to continue on the road of sanctions if there is no response from the Iranians," he told reporters. "If that continues these sanctions must be reinforced but at the same time we must have dialogue."

Iran said Tuesday it had started work to install thousands of new centrifuges to enrich uranium at its main nuclear plant, defying UN Security Council calls to freeze the sensitive process.

The West fears Iran could use uranium enrichment to make a nuclear weapon, and Tehran's refusal to suspend the process has been punished with three sets of UN Security Council sanctions and US pressure on its banking system.

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