Iran announced new "achievements" in its nuclear program on Tuesday as the United States warned that Tehran will face further international sanctions over its disputed nuclear work.

On the occasion to mark Iran's National Day of Nuclear Technology on Tuesday, Iranian President Mahmoud Ahmadinejad said his country has tested a new advanced centrifuge and started to install 6,000 new centrifuges at Natanz nuclear plant, according to the official IRNA news agency.

"Today a new machine was put to test," Ahmadinejad said in a televised speech Tuesday evening, adding that "It is smaller," but its capacity "is five times greater than the current machines."

The Iranian president called the development a major "breakthrough" in Iran's nuclear program and the "beginning of a speedy decline of the big powers' dominance in nuclear energy."

The president made the remarks after inspecting various sections of Natanz nuclear site in central Isfahan province, IRNA said.

Iran already has about 3,000 centrifuges in Natanz, and the new announcement showed Iran's latest defiance of international demands to halt its nuclear enrichment work.

The 20th day of the first month of the Iranian calendar year (Farvardin) which falls on April 8 this year, was announced as National Nuclear Technology Day by Ahmadinejad last year.

The day marks the achievement of Iranian scientists in producing 3.5 percent uranium enriched in Natanz facility two years ago.

Hours after Ahmadinejad's speech that Iran has begun installing 6,000 new centrifuges at its uranium enrichment plant, U.S. officials warned that Iran will face new international isolation and sanctions if it refuses to comply with UN Security Council resolutions over its disputed nuclear program.

"The Iranian government continues to be in violation of multiple United Nations Security Council resolutions and with each step it takes it continues to isolate its people and risk further international financial and diplomatic sanctions," U.S. National Security Council spokesman Gordon Johndroe told reporters.

With regard to Iran's nuclear issue, White House press secretary Dana Perino also vowed to increase global pressure on Iran.

"What we have decided to do as a community, as an international community is to continue to keep that pressure on," she said.

The United States and its Western allies fear that Tehran is trying to build nuclear weapons. Iran insists that its nuclear program is for peaceful purposes only.

The UN Security Council has imposed three sanctions against Tehran's nuclear program since Dec. 2006.

(Xinhua News Agency April 9, 2008)