Iran's new move to enrich uranium to a higher 20-percent level has aroused the concern of Western countries, with the U.S. threatening to impose "a significant regime of sanctions" with other major countries against the country.

An Iranian nuclear negotiator originally accepted a draft plan proposed by the U.N. nuclear watchdog agency -- the International Atomic Energy Agency (IAEA) -- in October, agreeing to ship the country's low-enriched uranium to Russia and France for the 20-percent-pure fuel rods for a Tehran reactor producing medical isotopes to treat cancer patients.

However, among the wide disputes and strong opposition in the Iranian parliament, Iran later balked and then rejected the arrangement, announcing on Sunday that it would produce its own higher-enriched uranium instead.

Iran says more than 850,000 people need the isotopes and radiography materials produced by the Tehran reactor for their illnesses.

Analysts believe President Mahmoud Ahmadinejad announced the uranium enrichment activities on the eve of the 31st anniversary of the 1979 Islamic Revolution, to coordinate the stances of various sides and to protect the internal solidarity of the regime.

Domestic media also think the decision would give more initiative to the Iranian government during its nuclear negotiations with the international community, and help it gain more bargaining chips against Western countries.

Western powers acted strongly against Iran's new move. U.S. President Barack Obama said Tuesday that Iran remains on the path of nuclear weapons, despite its denial, and the international community is moving "fairly quickly" toward imposing broader sanctions on Iran.

Obama said Iran's refusal to accept an U.N.-brokered nuclear fuel swap deal suggested that Iran is still trying to build nuclear weapons, despite the country's insistence that the nuclear enrichment is purely for civilian use.

Obama said the door is still open for Iran to come back to the negotiating table, but the U.S. is now mainly focused on sanctions.

"What we are going to be working on over the next several weeks is developing a significant regime of sanctions that will indicate to them how isolated they are from the international community as a whole," Obama said.

He also said the U.N. penalties are only one part of the international sanctions on Iran, hinting more economic sanctions could be applied by the European Union and individual countries over the next several months.

The British Foreign Ministry said Iran doesn't possess the technology to turn the higher-grade uranium into the fuel rods needed for the Tehran reactor.

Germany also raised the sanctions threat, while Britain said Iran's new plans would breach U.N. resolutions.

France also said Iran's action left no choice but to push harder for a fourth set of U.N. Security Council sanctions to punish Iran's nuclear defiance.

Even Russia, which is friendly with Iran and has opposed new sanctions, has expressed disappointment on Tehran's move, saying the enrichment work has raised new suspicions.

"Iran says it doesn't want to have nuclear weapons. But its actions, including its decision to enrich uranium to 20 percent, have raised doubts among other nations, and these doubts are quite well-founded," said Nikolai Patrushev, chief of Russia's Security Council.

Although a nuclear bomb requires about 90 percent purity of uranium, getting to 20 percent is a big step as low-level enrichment is the most time-consuming and difficult stage of the process, according to experts.