Iran is moving its production of higher-enriched uranium to a mountain bunker, where it plans to triple output by using more advanced centrifuges, state television reported Wednesday.

Iran says the announcement is a response to a letter Friday from Yukiya Amano, director general of the International Atomic Energy Agency, which reiterated “concerns about the possible military dimensions” of the Islamic republic’s nuclear energy program.

“Our answer is increased work in the sphere of nuclear technology and know-how,” Iranian nuclear chief Fereydoun Abbasi told reporters after a cabinet meeting.

Iran’s nuclear officials had signaled previously that the country’s most sensitive nuclear equipment would be moved to a site inside a mountain. But the predicted sharp increase in the production of uranium enriched to nearly 20 percent is a new development and will further heighten tensions between Iran and world powers distrustful of the nature of the country’s nuclear program.

Currently, Iran is enriching uranium at its Natanz site, where the bulk of the output is nuclear fuel enriched to 3.5 percent — suitable for powering reactors that generate electricity. The new location, named Fordo, is dug deep into a mountain next to a military base near the city of Qom. It was long kept secret but is now being monitored by the International Atomic Energy Agency, the U.N. nuclear watchdog. The IAEA says there are no centrifuges in the mountain bunker at present.

According to a February report by the IAEA, Fordo is to house at least 3,000 centrifuges, and Iran plans to feed uranium into them “by summer.” Iran says it will produce nuclear fuel enriched up to a level of nearly 20 percent using new, advanced enrichment equipment. The country says it needs the higher-enriched uranium to operate a 44-year-old U.S.-built nuclear test reactor that produces isotopes for use in nuclear medicine.

In his letter, the IAEA’s Amano called on Iran to grant the agency more access to dispel worries about the militarization of the country’s nuclear program.

“I also requested that Iran provide prompt access to relevant locations, equipment, documentation and persons,” Amano said in a statement Monday.

President Obama, in a joint news conference with German Chancellor Angela Merkel on Tuesday, said Iran is continuing to shun serious talks on its nuclear program and might face new sanctions by the United States and its allies.

“If the International Atomic Energy Agency this week determines again that Iran is continuing to ignore its international obligations, then we will have no choice but to consider additional steps, including potentially additional sanctions, to intensify the pressure on the Iranian regime,” Obama said.

On Wednesday, National Security Council spokesman Tommy Vietor expressed concern at Iran’s latest move, calling it a provocative step and urging the Islamic republic to reconsider.

“The decision would involve Iran’s stockpiling of even more near-20 percent enriched uranium without a credible use for this material in the near term,” he said.

Iran’s ambassador to the IAEA denied the accusations, calling them “politically motivated and unfounded,” the official Islamic Republic News Agency reported.

Iranian President Mahmoud Ahmadinejad also dismissed the accusations, saying that they were “dictated by Washington.” He warned Amano not to be biased against Iran and stressed that all of the country’s nuclear activities were being carried out according to international law.

“There is no brake and no reverse gear on our nuclear program,” Ahmadinejad told reporters Tuesday. Asked whether he would ever consider stopping the enrichment of uranium, a key demand of the United States and its allies, he replied, “No.”

Staff writer Scott Wilson in Washington contributed to this report.