Iran has increased the number of operating centrifuges at its uranium enrichment plant to 4,000, a top official said Friday, pushing ahead with the nuclear program despite threats of new UN sanctions. The number was up from the 3,000 centrifuges that Iran announced in November that it was operating at its plant in the central city of Natanz. Still, it is well below the 6,000 it said last year it would operate by summer 2008, suggesting the program may be behind schedule. Deputy Foreign Minister Ali Reza Sheikh Attar, who visited Natanz last week, said Friday that Iran was preparing to install even more centrifuges, though he did not offer a timeframe. "Right now, nearly 4,000 centrifuges are operating at Natanz," Attar told the state news agency IRNA. "Currently, 3,000 other centrifuges are being installed." The UN has already imposed three rounds of sanctions on Iran for its refusal to freeze its enrichment program, which can be used to produce either fuel for a nuclear reactor or the material needed for a nuclear warhead. In the process, uranium gas is spun in a series of centrifuges known as "cascades" to purify it. Lower levels of enrichment produce reactor fuel - which Iran says is the sole purpose of the program - but higher grades can build a weapon. The United States and its allies are likely to press the UN later this year for a new round of sanctions after Iran did not accept a package of economic and technological incentives in return for suspending enrichment. But they could face strong resistance from Russia after this month's crisis in Georgia deeply damaged ties between Washington and Moscow. Russian Prime Minister Vladimir Putin suggested his country's cooperation with the West on the Iran issue could be hurt by the Georgia tensions. Asked if Moscow might stop cooperation if it comes under increased pressure over Georgia, he told CNN that Russia is "working very consistently and diligently with its partners" on the Iran issue. But "if nobody wants to talk with us on these issues and cooperation with Russia is not needed, then for God's sake, do it yourselves," he said in the interview aired Thursday. Russia, which has close ties to Teheran, has long been reluctant to impose harsh sanctions - though it backed the past three rounds of limited financial sanctions. The International Atomic Energy Agency, the UN's nuclear watchdog, declined to comment on the latest Iranian announcement. By reaching 4,000 centrifuges, the program is moving into an industrial-scale program that could churn out enough enriched material for dozens of nuclear weapons. Experts, however, say Iran would need to change the way centrifuges are operating to enrich uranium to high, weapons-grade levels, something that would be difficult since the Natanz facility is under IAEA video surveillance. Last month, Iranian President Mahmoud Ahmadinejad said Iran possessed 6,000 centrifuges, though he did not specify how many were operating. He also suggested that negotiations with the UN had raised a possible compromise whereby the enrichment program could continue as long as it was not expanded beyond 6,000 centrifuges. However, the IAEA and the countries involved in the nuclear issue - the US, Britain, France, Germany, China and Russia - have not shown any public sign that such a compromise was on the table. EU foreign policy chief Javier Solana presented Iran with the incentives offer in June. Iran finally sent a reply in August, but the US and its allies said the response did not directly address the offer and considered it a rejection. The workhorse of Iran's enrichment program is the P-1 centrifuge, which is run in cascades of 164 machines. But Iranian officials confirmed in February that they had started using the IR-2 centrifuge, which can churn out enriched uranium at more than double the rate. Iran says it plans to move toward large-scale uranium enrichment that will ultimately involve 54,000 centrifuges.