An Iranian opposition group claimed Thursday to have discovered the location of a secret factory that manufactures high-tech equipment for Iran’s nuclear program, a facility the group says is disguised as a tool-making plant.

The National Council of Resistance of Iran said the alleged plant makes centrifuge parts for Iran’s uranium enrichment program and is closely tied to Iran’s Defense Ministry. The dissident group also claimed that Iran already has made components for 100,000 centrifuge machines, far more than is needed to supply the country’s known uranium facilities.

“This is a clear indication that there are other secret sites out there, either undergoing construction or perhaps already completed,” Alireza Jafarzadeh, a consultant and former spokesman for the NCRI, told reporters after unveiling satellite photos of the site 80 miles west of Tehran.

U.N. nuclear officials have long known that Iran is operating factories for centrifuge parts, but Iranian officials have never allowed visits by U.N. inspectors or even revealed the location of the facilities. Centrifuges are fast-spinning machines used to make enriched uranium, a key ingredient in both nuclear reactor fuel and nuclear weapons.

The opposition group identified a cluster of three buildings inside a small industrial park as Iran’s main production center for centrifuge parts since 2006. The complex is dubbed “Taba,” after a cutting-tool plant that once occupied the site, and is under heavy security, Jafarzadeh said.

He said some components for Taba were being manufactured at a nearby facility called Shahid Shafi’zahdeh Industrial Complex, a subsidiary of the Iranian Defense Ministry’s Aerospace Industries Organization.

Other than labeled satellite photos, the dissidents offered no evidence to back their claims. The NCRI and its operational wing — the Mujaheddin-e Khalq — have revealed the existence of other secret Iranian nuclear sites in the past, and the group was the first to publicly disclose the existence of Iran’s underground uranium enrichment site at Natanz.

Jafarzadeh said the group has shared the new information with both the U.S. government and the International Atomic Energy Agency, and he called on Iran to allow inspectors into the Taba facility to remove any doubt about the nature of the site. There was no immediate reaction to the NCRI’s claim from U.S. or U.N. officials.

“The easy way to verify this is to open the site to the IAEA so they can inspect it,” he said.

Iran, which insists that its nuclear program is entirely peaceful, contends that it is not obligated under international treaties to open is centrifuge production facilities to outsiders for inspection.

About 9,000 centrifuges are currently installed at the Natanz facility, including about 1,000 machines that were rushed into production in the past two years to replace damaged equipment after a series of apparent cyber-attacks on Natanz.