(TJV NEWS) Iran is reinforcing its underground nuclear facilities just days before a new round of negotiations with the Trump administration, according to the Institute for Science and International Security (ISIS), a Washington-based non-profit that monitors global nuclear activity.

As NBC News noted, Iran has refused to comply with U.S. demands for a complete suspension of uranium enrichment — a sticking point that could push military action closer, President Donald Trump warned earlier this week.

ISIS, citing recent satellite imagery, reported that Iran has expanded a heavy security perimeter around Mt. Kolang Gaz La, a mountain that houses two major underground tunnel complexes linked to the Natanz nuclear facility. The construction, which includes newly graded roads and prefabricated wall panels, isolates a significant portion of the mountain and limits access to the tunnel entrances. Analysts from ISIS pointed out that the perimeter connects with existing security barriers around Natanz and appears reinforced by trenches, likely intended for surveillance and communications infrastructure.

While the tunnels may not yet be fully operational, ISIS experts said it is difficult to determine their status based on satellite images alone. They explained that one tunnel, initially built in 2007, sat dormant for a decade before being revived around 2020. The second was constructed after a 2020 explosion destroyed Iran’s previous underground centrifuge facility.

Critically, Iran has not permitted inspectors from the International Atomic Energy Agency (IAEA) to visit either tunnel complex since 2007. Speaking Thursday, IAEA Director General Rafael Grossi urged Tehran to clarify the purpose of the new security installations. Grossi said Iran’s only response was to declare the matter “none of your business,” as NBC News reported.

Despite the tensions, Grossi expressed cautious optimism that U.S. envoy Steve Witkoff could still broker a deal. However, Secretary of State Marco Rubio reiterated on Wednesday that Washington’s position remains firm: Iran must cease all uranium enrichment activities.

“If Iran wants a civil nuclear program, they can have one — the same way many countries do — by importing enriched material,” Rubio said, emphasizing that such arrangements are standard among nations with peaceful nuclear ambitions.

Iranian officials, meanwhile, signaled no willingness to compromise on enrichment. “The core issue of enrichment itself is not negotiable,” Foreign Minister Abbas Araghchi declared, according to reports.

Iran’s delegation, including senior diplomat Kazem Gharibabadi, arrived in Muscat, Oman, on Friday to begin a third round of technical negotiations. Earlier rounds in Italy and Oman were described by both sides as “productive.”

The U.S. delegation will be led by Michael Anton, President Trump’s new head of policy planning at the State Department.

Iranian Supreme Leader Ayatollah Ali Khamenei, once a fierce critic of engaging the Trump administration, appears to be softening his stance. According to reports cited by NBC News, Khamenei has recently scolded hardliners within his government who oppose a negotiated settlement.

Iranian Foreign Minister Araghchi reportedly told U.S. negotiators last week that reaching a full comprehensive agreement within the Trump administration’s 60-day deadline would be difficult, but an interim deal might be achievable. Iran’s mission to the United Nations denied the report, and the U.S. State Department declined to comment.