VIENNA — In a defiant move ahead of nuclear talks, Iran has announced plans to vastly increase its pace of uranium enrichment, which can make both reactor fuel and the fissile core of warheads. Eager to avoid scuttling those negotiations, world powers are keeping their response low-key.

Iran told the International Atomic Energy Agency of its intentions last week, and the IAEA informed member nations in an internal note seen by The Associated Press on Thursday.

The brief note quoted Iran as saying new-generation IR2m “centrifuge machines ...will be used” to populate a new “unit” — a technical term for an assembly that can consist of as many as 3,132 centrifuges.

It gave no timeframe. A senior diplomat familiar with the issue said work had not started, adding that it would take weeks, if not months, to have the new machines running once technicians started putting them in. He demanded anonymity because he was not authorized to divulge confidential information.

Mark Fitzpatrick, a non-proliferation expert and former senior official at the U.S. State Department, described the planned upgrade as a potential “game-changer.”

“If thousands of the more efficient machines are introduced, the timeline for being able to produce a weapon’s worth of fissile material will significantly shorten,” said Fitzpatrick, of the International Institute for Strategic Studies.

“This won’t change the several months it would take to make actual weapons out of the fissile material or the two years or more that it would take to be able to mount a nuclear warhead on a missile, so there is no need to start beating the war drums,” he said. “But it will certainly escalate concerns.”

The planned upgrade could burden international efforts to coax Tehran into scaling back its nuclear activities and cooperating with the agency’s attempts to investigate its suspicions of secret weapons work. Talks are tentatively set for next month with a date and venue still open.

Iran insists it does not want nuclear arms and argues it has a right to enrich uranium for a civilian nuclear power program. But suspicion persists that the real aim is nuclear weapons. The Islamic Republic hid much of its nuclear program until it was revealed from the outside more than a decade ago. A deadlock in the IAEA’s probe of Iran’s nuclear program has furthered suspicions of a clandestine pursuit of atomic weapons.

Defying U.N. Security Council demands that it halt uranium enrichment, Iran has instead expanded it. Experts say Tehran already has enough enriched uranium to be able to turn it into weapons-grade material for several nuclear weapons.

The Iranian plan was condemned by Israel, which sees Iran’s nuclear program as an existential threat and has said it would use all means to stop it from reaching weapons capability.

“While the world is discussing where and when the next meeting with Iran will be, Iran is rapidly advancing towards obtaining a nuclear bomb,” said a senior official from Prime Minister Benjamin Netanyahu’s office. “The international community cannot allow Iran to arm itself with a nuclear weapon.”

The official demanded anonymity because he said he was not allowed to comment publicly on the issue.

Phone calls seeking comment from Ali Asghar Soltanieh, Iran’s chief IAEA delegate, went to his voicemail.

The envisaged centrifuge upgrade potentially complicates planned talks next month during which the United States, Russia, China, Britain, France and Germany are expected to press Tehran to cut back on uranium enrichment, and Iran is likely to seek relief from sanctions cutting into its oil sales and financial transactions.

Iran may be hoping that its tough line on enrichment will force further concessions from the six, which over the past year have scaled down their demands from a total enrichment freeze. More recently, after a series of inconclusive meetings, they’ve asked merely for a halt to Iran’s higher-enrichment program.

Yousaf Butt, professor and scientist-in-residence at the Monterey Institute of International Studies, who supports Iran’s right to enrich uranium, said Tehran was “using the only leverage it has — its enrichment program — as a means to coax some sanctions relief.”

There was no indication late Thursday that the six powers were ready to go that way. But moderate reactions from some suggested they were eager to keep negotiation channels open.

The British Foreign Office confirmed that Iran had informed the International Atomic Energy Agency of its plan, and described it as “a cause for concern,” noting it breached both U.N. Security Council and IAEA board resolutions urging Iran to curb enrichment.

But it avoided linking the move to the next round of talks. Instead the statement expressed hope that Iran would soon respond to the six powers on a time and place for a meeting, adding: “We hope that Iran will agree to talks quickly and come to the table ready to engage and negotiate seriously.”

In Moscow, Russian Foreign Minister Sergei Lavrov noted Thursday that Moscow and its fellow U.N. Security Council members “have called on Iran to freeze enrichment operations during the negotiations.” But he too avoided any direct suggestion that the planned Iranian centrifuge update would upend such talks.

The White House said the move by Iran did not come as a surprise, describing it as a further escalation and continuing violation of Iran’s international obligations.

“It would mark yet another provocative step by Iran, and will only invite further isolation by the international community,” said White House spokesman Jay Carney. “We continue to believe that there is time and space for diplomacy to work, but actions like this only undercut the efforts of the international community to resolve its concerns.”

The European Union’s top foreign policy official, Catherine Ashton, said she is confident negotiations over Iran’s nuclear program will resume soon. Ashton has convened past meetings, and her spokesman had suggested last week that Iran was delaying by setting new preconditions and not agreeing to a venue.

A Western diplomat accredited to the U.N. agency said IAEA delegation heads from the U.S. and its allies exchanged views over Iran’s plans Thursday and agreed to await further developments. He also demanded anonymity because he was not authorized to talk about the issue.

While acknowledging that the Iranian plan was of concern, he noted that Tehran had set no date for installing the new centrifuges. That, he said, gave the international community breathing space.

Iran says it is enriching only to power reactors and for scientific and medical purposes. But because of its nuclear secrecy, many countries fear that Iran may break out from its present production that is below the weapons-grade threshold and start enriching uranium to levels of over 90 percent, used to arm nuclear weapons.

Tehran now has more than 10,000 centrifuges enriching uranium at its main plant at Natanz, 225 kilometers (140 miles) southeast of Tehran, to fuel grade at below 4 percent. Its separate Fordo facility, southwest of Tehran, has close to 3,000 centrifuges — most of them active and producing material enriched to 20 percent, which can be turned into weapons-grade uranium much more quickly.

Iran has depended on domestically made and breakdown-prone IR-1 centrifuges whose design is decades-old at both locations up to now, but started testing more sophisticated prototypes in the summer of 2010.

David Albright, whose Washington-based Institute for Science and International Technology serves as a resource for some U.S. government branches, estimated in a 2011 report that 1,000 of the advanced machines “would be equivalent to about 4,000-5,000 IR-1 centrifuges” in production speed.

Separately from the talks between Iran and the six powers, IAEA experts are scheduled to visit Tehran on Feb. 13 in their more-than-yearlong effort to restart the probe of the weapons allegations.

The British statement urged Iran to “take serious practical steps to cooperate with the IAEA on all matters of substance relating to the possible military dimensions to its nuclear programme.”

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Associated Press writers Josh Lederman in Washington, Cassandra Vinograd in London, Aron Heller in Jerusalem, and Jim Heintz in Moscow contributed.