“If the international community banded together to pressure the Iranian government, I believe that sanctions and pressure can still walk,” Gates said in Rome after meeting with his Italian counterpart Ignazio La Russa.

Mr. Gates has held the remarks after Iranian President Mahmoud Ahmadinejad has ordered Sunday the start of production of highly enriched uranium in Iran.

But Ahmadinejad said that Iran was ready agreement on the exchange of nuclear fuel with the world powers.

Ahmadinejad made the announcement two days after the Iranian Minister of Foreign Affairs Manouchehr Mottaki has said Tehran wanted to reach an agreement on the transfer of uranium to the world power in the near future.

But the United States and Germany said Saturday they saw no sign of the concession from Iran on its nuclear program, and they could opt for increased pressure on Tehran.

“Iran has formally informed (the International Agency of Atomic Energy Agency, IAEA) of its plans to launch its activities of enrichment to reach a purity of 20%,” said the Iranian envoy to IAEA Ali Asghar Soltanieh, Fars.

In the letter, Iran asked IAEA inspectors to monitor the enrichment process, because all the country’s nuclear activities are under observation of the IAEA, said Soltanieh quoted by Fars.

The most highly enriched uranium is used as fuel for research reactor in Tehran, according Soltanieh.

The head of the Organization for Atomic Energy of Iran (AEOI), Ali Akbar Salehi, said Sunday that Iran will begin to enrich its uranium on Tuesday reported the satellite TV station Iranian Press TV.

Iran informed the IAEA of its plan to enrich its uranium enrichment Monday and will begin Tuesday, reported Press TV.

Earlier Sunday, Iranian President Mahmoud Ahmadinejad has ordered the AEOI to start work on uranium enrichment to reach a purity of 20%, reported news agency Mehr.

However, Mr Ahmadinejad said Iran is ready to share its nuclear fuel with the world powers.

Obama said that Iran had refused to accept an agreement uranium processing the UN, which is, according to him, “the most obvious attempt” by the international community to cooperate with Tehran.

He said that because of Tehran’s refusal to commit, the next step is to move to sanctions.

He accused Iran of pursuing “a path leading to the militarization, stressing that what is unacceptable not only to the United States, but also for the international community

“What we’re going to work in the coming weeks is to develop a system of sanctions siginficatives” said President Obama.

He said his administration will address a variety of ways in which countries report on Iran that its approach is unacceptable, and that the UN will be one aspect of this broader effort.

He expressed confidence that the international community is united around the bad behavior of Iran, to more pressure on Tehran.

Obama made the remarks during an unexpected appearance in the press room of the White House, where spokesman Robert Gibbs was supposed to hold a regular press briefing.

Iran began Tuesday uranium enrichment to 20%.

An agreement brokered by the International Atomic Energy Agency Nuclear Safety of the UN, provides shipment by Iran of its core low-enriched uranium to Russia and France, where it is processed into fuel rods with a purity of 20 percent.

Iran is the center of an international controversy over its nuclear program. The United States and its Western allies accuse Iran of secretly developing atomic weapons under cover of a civilian program. Iran denies the charge and says its nuclear program is only used for peaceful purposes.