Iran has refused to stop enriching uranium as demanded by a United Nations Security Council resolution, the head of the UN's atomic watchdog said Thursday.

"Iran has not suspended its enrichment-related activities," the International Atomic Energy Agency said in a report.

In the report, written by IAEA director general Mohamed ElBaradei, the agency says Iran has expanded its enrichment activities, including setting up hundreds of uranium-spinning centrifuges in an underground hall and building a reactor that will use heavy water and a heavy water production plant.

Enriched uranium and plutonium produced by heavy water reactors can produce the fissile material used in nuclear warheads.

The six-page report's conclusions, which were expected, mean Iran could face tougher UN sanctions, including a travel ban on senior Iranian officials and restrictions on the country's businesses.

The head of Iran's Atomic Energy Organization, Mohammed Saeedi, said Thursday Iran considers the Security Council request an infringement of its rights.

"Iran considers the [IAEA demand for] suspension as against its rights, the Nuclear Non-proliferation Treaty and international regulations," said Mohammed Saeedi, quoted in the official Islamic Republic News Agency.

The UN imposed an earlier set of sanctions on Iran on Dec. 23 after Tehran refused to freeze all its enrichment-related activities.

The sanctions banned the sale of technology and materials to Iran that could be used in that country's nuclear and missile programs. A 60-day grace period granted to Tehran expired on Wednesday.

Will use all channels: Rice

U.S. Secretary of State Condoleezza Rice said Thursday that Washington, which believes Tehran is developing nuclear weapons under the cover of a nuclear-energy program, would use "available channels" to get Iran back to the negotiating table.

"We reconfirmed we will use available channels and the Security Council to try to achieve that goal," she said following a breakfast meeting in Berlin with her counterparts from Germany, Russia and the European Union.

As a signatory of the Nuclear Non-Proliferation Treaty, Iran is permitted to enrich uranium for peaceful purposes, such as energy development.

Iran's president on Wednesday said his country has the right to pursue nuclear energy.

"The enemy is making a big mistake if it thinks it can thwart the will of the Iranian nation to achieve the peaceful use of nuclear technology," Iranian state TV's website quoted President Mahmoud Ahmadinejad as saying Wednesday.

On Tuesday, Ahmadinejad said Iran would halt its enrichment program if Western countries did the same, an offer Washington rejected.

With files from the Associated Press