Tehran could face tougher economic sanctions if it goes ahead with its uranium enrichment plans, a senior Russian MP said on Monday.

Earlier in the day, Iran notified the UN nuclear watchdog of plans to produce higher enriched uranium, saying it could not wait any longer to reach an agreement on international processing of its uranium for a reactor in Tehran.

"The international community will not support this position. The issue of tighter economic sanctions against Tehran could be raised," said Konstantin Kosachyov, head of the State Duma international affairs committee.

He added that the international community should send Iran a "strong, consolidated signal" about the unacceptability of such a move, which he described as a "setback."

Ali Asghar Soltanieh, Tehran's envoy to the International Atomic Energy Agency, told state-owned Al-Alam television from Vienna that an official letter on the start of the 20% uranium enrichment activities to provide the research reactor in Tehran with fuel has been handed over to the IAEA.

Under a plan drawn up by the IAEA last October, the Islamic Republic was to ship out its low-enriched uranium to Russia, where it would be enriched and then sent to France where it would be made into fuel rods for an Iranian reactor.

The proposal was approved by the six international powers negotiating with Iran over its nuclear program, but Tehran stalled and then rejected the plan, suggesting it could consider a simultaneous swap of its low-enriched uranium for 20%-enriched uranium, but that the exchange should be simultaneous and would have to take place on its own territory.

Iran's announcement could spur the UN Security Council to agree on a fourth set of sanctions over its nuclear activities, which Western powers fear are aimed at building weapons. Tehran insists its nuclear program is for civilian power generation.

Russia has backed the diplomatic approach but in recent months has appeared to soften its opposition to further sanctions, although China has continued to resist a tougher approach.

Salehi's announcement of plans to enrich uranium to 20%, the level required to be used as fuel in reactors, came hours after orders from hardline President Mahmoud Ahmadinejad.

Salehi, however, said that Tehran will stop the enrichment program if a deal on the enrichment of uranium can be agreed with the so-called Iran Six - Russia, China, the United States, Britain, France and Germany.