Over the weekend, Iranian Foreign Minister Mottaki rebuffed a uranium swap plan proposed by the West. In Tehran, President Mahmoud Ahmadinejad ordered his scientists to begin enriching uranium to 20 percent. It is now time to impose tough new sanctions, say German commentators.

The nuclear dispute between the West and Iran escalated over the weekend after Tehran said it would intensify its nuclear program and effectively rebuffed Western proposals for a deal by restating conditions deemed unacceptable by the international community.

Raising fears that Iran is trying to develop nuclear weapons, President Mahmoud Ahmadinejad announced on Sunday that Iran would start enriching uranium to 20 percent for a Tehran research reactor, which Iran claims is for producing medical isotopes used for the diagnosis and treatment of diseases.

Analysts said that would bring Tehran a big step towards the enrichment of at least 90 percent needed for weapons-grade uranium. Western powers have been trying to persuade Iran to refrain from nuclear enrichment by offering to swap Iran's low-enriched uranium for higher-grade nuclear fuel. But the two sides have failed so far to agree on how to implement the plan.

On Friday, Iranian Foreign Minister Manouchehr Mottaki had raised hopes that Iran might be preparing the ground for a deal when he paid a surprise visit to the Munich Security Conference. But he merely restated conditions for the proposed swap - that any fuel exchange must be simultaneous and that Iran would determine the quantities involved.