The United States warned Iran Thursday that the installation of next-generation centrifuges at one of its main nuclear plants, as reported by the UN atomic agency, would be a "provocative step."

The installation "would be a further escalation and a continuing violation of Iran's obligations under the relevant UN Security Council resolutions and IAEA board resolutions," State Department spokeswoman Victoria Nuland said.

"So it would mark yet another provocative step," she said.

The International Atomic Energy Agency, the UN nuclear watchdog, on Thursday said Tehran had begun installing the new IR-2m centrifuges earlier this month at the Natanz plant.

"This is the first time that centrifuges more advanced than the IR-1 have been installed" at the plant in central Iran, an IAEA report said.

The report comes five days before Iran is set to sit down with world powers in Kazakhstan for the latest round of talks on the Islamic republic's nuclear program, which the West and Israel say is a front for weapons development.

Tehran insists its program is strictly for peaceful purposes.

The talks between the so-called P5+1 -- the United States, China, Russia, Britain, France and Germany -- and Iran will be the first since June, when three rounds of meetings ended in stalemate in Moscow.

Nuland, who said the report of new centrifuges were no surprise, urged Iran to consider "another path... the diplomatic path."

"They have an opportunity to come to those talks ready to be serious, ready to allay the international community's concerns, and we hope they take that opportunity," she said.

Iran's new nuclear equipment a 'serious concern': Britain
London (AFP) Feb 21, 2013 - Britain expressed "serious concern" on Thursday at news that Iran had installed new nuclear equipment, saying it was another sign of Tehran's refusal to address Western fears about its nuclear programme.

Five days before international talks between Iran and six world powers, the International Atomic Energy Agency (IAEA) said in a new report that Tehran has begun installing next-generation equipment at one of its main nuclear plants.

"Iran's installation of more advanced centrifuges at its enrichment plant at Natanz is of serious concern," said Foreign Office minister Alistair Burt.

"It represents yet another breach of United Nations Security Council and IAEA Board resolutions, and is another signal that Iran has no intention of providing the necessary reassurance to the international community that its nuclear programme is for purely peaceful purposes."

He added: "The timing of this move -- immediately before the IAEA board of governors meeting and before E3+3 talks with Iran in Almaty, Kazakstan next week -- concerns and disappoints us.

"We trust that Iran will come to talks in Almaty willing to negotiate meaningfully, and we urge Iran to respect all relevant resolutions and cooperate fully with the IAEA."

Iran denies seeking atomic weapons but many in the international community suspect otherwise, and the UN Security Council has passed several resolutions calling on Iran to suspend all uranium enrichment.

Iran and six world powers -- the US, China, Russia, Britain, France and Germany -- are due to hold talks in Kazakhstan on February 26, the first such discussions since three rounds of meetings last year in Moscow ended in stalemate.