(CNSNews.com) – Kicking off what promises to be a significant week in Iran, President Mahmoud Ahmadinejad on Sunday ordered the head of the national nuclear agency to begin boosting uranium enrichment to new levels.

Defense Secretary Robert Gates in response renewed calls for the international community to unite around sanctions against the regime Tehran, while the British government called the move “a matter of serious concern” saying upping enrichment to 20 percent would breach U.N. Security Council resolutions.

Ahmadinejad’s televised announcement comes four days before Iran marks the anniversary of the Islamic revolution. Opposition leaders have called for supporters to take to the streets on Thursday and security officials have vowed to crack down if they do.

Ahmadinejad has also signaled that the anniversary will herald an important announcement by the Iranian government, sparking speculation that he may reveal further advances in the nuclear program.

The centrifuges at Iran’s Natanz fuel enrichment plant currently enrich uranium’s U-235 isotope to 3.5 percent – reactor grade. Iran now says it plans to enrich up to 20 percent, the upper end of the required level for research reactors like the Tehran-based medical research facility. Weapons-grade uranium is enriched at more than 90 percent.

Foreign ministry spokesman Ramin Mehman-Parast told the Fars news agency later Sunday that Iran was entitled under international conventions to enrich to 20 percent, and that the work would be done under International Atomic Energy Agency (IAEA) supervision.

Ahmadinejad’s comments may be a sign of brinkmanship aimed at forcing the West to accept Iranian terms in a dispute over sending nuclear fuel abroad for enrichment.

In a bid to end the long running nuclear standoff, the U.S. and other leading powers last year put forward a plan that would see Iran send most of its low-enriched uranium (LEU) abroad for conversion to nuclear fuel, which would then be returned to Iran for use in its research reactor.

Iran rejected the terms, saying the West should either sell nuclear fuel directly to Iran, or exchange nuclear fuel for Iran’s LEU in small batches rather than all at once. But that would rob the agreement of its main goal for the West – to deprive Iran of the bulk of its LEU stockpile so as to prevent future enrichment to weapons-grade levels.

Last week Iran hinted that a breakthrough on an agreement was imminent, but critics dismissed the move as another ploy designed to buy time and throw into disarray U.S. attempts to get China and others to back sanctions.

Protests loom

Speaking in Italy after Ahmadinejad’s comments on Sunday, Gates called for cooperation from key countries. He did not name them, but China has long resisted sanctions against Iran, a key energy supplier.

“If the international community will stand together and bring pressure to bear on the Iranian government, I believe there is still time for sanctions and pressure to work,” Gates said.

He implied that sanctions under consideration would not include those being pushed by U.S. lawmakers targeting Iran’s gasoline imports. “Pressures that are focused on the government of Iran, as opposed to the people of Iran, potentially have greater opportunity to achieve the objective,” Gates said.

Proponents of gasoline sanctions argue that hitting Iran where it hurts may be the best way to resolve the crisis peacefully.

On the other hand, some Iran analysts have warned that sanctions which adversely affect ordinary Iranians will merely strengthen the government’s position and undermine the opposition that grew out of Ahmadinejad’s disputed re-election last summer.

That opposition is gearing up for big protests on Thursday, the 22nd of Bahman on the Persian calendar, when Iranians mark the 1979 revolution that replaced the monarchy with the Islamic regime headed by Ayatollah Ruhollah Khomeini. Ahmadinejad is due to deliver a speech at a public square in Tehran.

“Green movement” leaders Mir-Hossein Mousavi and Mehdi Karroubi have invited supporters to demonstrate, and a group of human rights and democracy advocates also issued a statement calling for protests focusing on the recent sentencing to death of opposition members. Two men were executed late last month, accused of plotting to overthrow the Islamic republic. Another nine are on death row.

As the anniversary approaches, security figures have stepped up threats against opposition supporters, whom the government accuses of doing the bidding of Iran’s foreign foes.

On Sunday, judiciary head Ayatollah Sadegh Larijani issued a new warning to opposition supporters, vowing that anyone committing “counter revolutionary acts” would be dealt with severely.

Iran’s police chief, Brig.-Gen. Esmail Ahmadi Moqaddam, in separate comments said the security forces had “precise information” about the opposition’s plans for Thursday and would “defuse all enemies’ plots.”

He praised the police, the Islamic Revolution Guards Corps (IRGC), the Basij militia and other security agencies for showing no hesitation “in dealing with the recent conspiracy plots.”

Meanwhile Iran’s intelligence ministry announced that seven “agents” linked to Radio Farda had been arrested during an “operation.” It said they had been trained in Turkey and Dubai, receiving training in spreading lies and disrupting public order.

The ministry described the radio station as “a counter-revolutionary media which belongs to CIA.”

Radio Farda is a U.S.-funded Farsi-language broadcaster with offices in Washington and Prague. Attempts to get comment from the station were unsuccessful.