Iran is proclaiming significant gains in its nuclear program, progress that Western officials and experts say could effectively erase setbacks from recent cyber attacks and shorten the timeline for acquiring nuclear weapons.

Scientists from Iran’s atomic energy program, in announcements over the past three days, said they have successfully tested advanced centrifuges for enriching uranium and are less than a month away from starting the country’s first commercial nuclear reactor. The announcements, linked to the observance of “nuclear technology day” in Tehran, underscore recent assessments by intelligence officials and Western nuclear experts suggesting that Iran is preparing to speed up its production of enriched uranium.

Although many of the advances have not been fully implemented, the apparent progress has prompted some experts to redraw their forecasts for how quickly the country could build an atomic arsenal if it chose to do so.

The pronouncements also appear intended to counter perceptions that Iran’s nuclear program has been hobbled by a computer worm that heavily damaged the country’s main uranium enrichment facilities in a series of attacks in 2009 and 2010. During a weekend ceremony lauding the accomplishments, President Mahmoud Ahmadinejad declared that the “Iranian nation cannot be defeated,” despite sanctions and other threats.

“Not only should we be able to use all our capacities and potentials in nuclear technology, we should also export nuclear know-how,” Iran’s semiofficial broadcaster Press TV quoted the Iranian leader as saying.

The advanced centrifuges tested by Iran have been under development for several years. Experts say the new machines are far more sophisticated than the 1950s-era technology Iran has been using and will be far more efficient than their predecessors. According to the first reliable published estimates, the increase in the production of enriched uranium could be huge — an increase in output of at least 600 percent per machine.

“If they can get the new machines performing well, and in large numbers, it will make a big difference,” said Olli Heinonen, a former nuclear safeguards chief for the International Atomic Energy Agency, the U.N. nuclear watchdog agency.

In theory, a few hundred of the new machines could produce enough enriched uranium for a nuclear weapon in less than a year, he said.

Iran quietly notified U.N. inspectors in January that it was moving forward with plans to phase in hundreds of the sophisticated centrifuges — models dubbed IR-2M and IR-4 — at its main enrichment plant in the city of Natanz. On Saturday, Fereydoun Abbasi, the head of the Atomic Energy Organization of Iran, said the machines had been tested and were ready for use.

Abbasi also announced that Iran’s first commercial nuclear reactor, at Bushehr, will begin operating as soon as May 5 after technicians overcome problems with the reactor’s fuel. He disclosed the start of a new production line for uranium oxide, the material from which nuclear fuel rods are made.

Neither the United States nor the IAEA have published performance estimates for Iran’s next-generation centrifuges, but a U.S. intelligence official knowledgeable about Iran’s nuclear program did not dispute Heinonen’s observations.

“U.S. intelligence officials share the IAEA’s concern” about Iran’s expanding capabilities, the official said, speaking on the condition of anonymity.

Natanz has more than 8,000 centrifuges to enrich uranium, ostensibly for nuclear reactor fuel. But those machines have been notoriously unreliable and prone to attack.

In late 2009 and early 2010, a computer worm known as Stuxnet penetrated the computer system at Natanz. Although the cyber attack appears to have damaged as many as 1,000 machines, Iran has moved quickly to replace broken equipment and has continued to process uranium at a steady pace.

Heinonen, who until last year oversaw the IAEA’s teams of inspectors in Iran, recently presented performance estimates for the IR-2M during a seminar held by arms-control advocates in Washington.

Using an analysis that he said drew from “multiple sources,” Heinonen calculated that the new machines would produce enriched uranium at a slightly higher rate than comparable machines made in Pakistan and North Korea and more than six times as fast as the IR-1 centrifuge currently used by Iran.

Iran, which began enriching uranium on an industrial scale in 2007, is now thought to possess enough low-enriched fuel to make at least two bombs if the material were processed further. The country has consistently maintained that it does not intend to make nuclear weapons.

Heinonen’s figures are in line with Iran’s estimates for the capability of the new machine, which Iranian scientists have been testing since 2009.

The IR-1 machines the nation uses are based on a 1950s Dutch design that was stolen by Pakistani scientist Abdul Qadeer Khan and sold to Iran decades ago. The IR-1 is relatively slow and inefficient and notoriously unreliable.

Although U.S. officials have long suspected that Iran is capable of making better centrifuges, Iranian scientists have struggled to obtain the kinds of specialized materials needed to build them. The IR-2M, for example, is constructed largely from a carbon-fiber material similar to the Kevlar used in modern military helmets and body armor. Intelligence agencies think that Iran is not capable of making the material indigenously in significant quantities, and Iran has been repeatedly thwarted in its efforts to buy carbon fiber abroad.

Heinonen, however, noted that U.N. inspectors never were able to determine how much carbon fiber Iran managed to acquire before international sanctions dried up the market for such advanced materials. The IAEA also knows little about how and where the Iranians are building their new machines, he said.

“I think they’re probably limited in their ability to get these materials,” Heinonen said, “but the question is: How much do they already have?”