Top Russian security official Sergei Shoigu landed in Iran on Tuesday for talks with his counterpart just one day after reports surfaced suggesting the U.S. and the U.K. are increasingly concerned over an alleged nuclear deal between Tehran and Moscow. 

Details of Shoigu’s meeting in Iran remain scarce, but U.S. officials have increasingly begun sounding the alarm that the burgeoning relationship between Iran and Russia amid the war in Ukraine may have reached concerning new levels. 

Secretary of State Antony Blinken first referenced these concerns last week during a visit to the U.K., where he confirmed reports that Iran had supplied Russia with short-range ballistic missiles to aid its continued war effort against Kyiv. 

Security Council’s Secretary Sergei Shoigu in St. Petersburg, Russia, Sept. 12, 2024. (Sputnik/Kristina Kormilitsyna/Kremlin via Reuters)

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But in comments that largely fell under the radar given the confirmation that ballistic missiles had been given to Moscow, Blinken also said, “Russia is sharing technology that Iran seeks – this is a two-way street – including on nuclear issues as well as some space information.”

A report by The Guardian on Monday suggested that President Biden and U.K. Prime Minister Kier Starmer allegedly discussed the potential of a secret deal having been forged in which Russia has agreed to provide Iran with the technological know-how it needs to develop a nuclear weapon. 

Nuclear experts, including the U.N.’s own watchdog, the International Atomic Energy Agency (IAEA), have warned that Tehran has continued to develop its nuclear program unchecked for the last three and half years.

Iran is said to have increased its stockpiles of highly enriched uranium to levels of 60% purity – just shy of weapons-grade uranium, which is achieved with 90% purity levels.  

While information surrounding Shoigu’s meeting Tuesday remains unknown, his trip came just days after he traveled to fellow nuclear-armed nation, North Korea, and met with leader Kim Jong Un in Pyongyang.

North Korean leader Kim Jong Un meets with a delegation led by Sergei Shoigu, in this photo released by North Korea’s official Korean Central News Agency, Sept. 14, 2024. (KCNA via Reuters )

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Details of that trip also remain murky, but reports suggested Shoigu’s trip was an opportunity to deepen the Russia-North Korea partnership following the signing of a mutual defense treaty in June earlier this year.

Western nations have accused North Korea of supplying Russia with arms to aid its war effort in Ukraine, and concerns have mounted that Pyongyang could escalate its military deliverables to Moscow. 

The U.S. and its Western allies have pledged to hold nations accountable for aiding Russia in its illegal war in Ukraine, but Shoigu’s trips with the top adversarial nations coincided with threats leveled by Putin at Washington last week.

Neither the U.S. nor the U.K. have lifted their strike bans on Ukrainian supplied long-range weapons in order to permit Kyiv to strike deep into Russia – a move it argues is critical for ending the war with Moscow. 

Amir Ali Hajizadeh, commander of Aerospace Force of the Islamic Revolutionary Guard Corps, gives a speech as Iran presents its first hypersonic ballistic missile in Tehran on June 6, 2023. (Sepah News/Handout/Anadolu Agency via Getty Images)

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But Putin last week said any move by the U.S. and its NATO allies to reverse these strike bans will be seen as its direct involvement in the conflict and would mean they are “at war” with Russia – possibly extending the threat of a Russian strike outside of Ukraine. 

Putin has made these threats against the West before, though no strike ban reversals were announced during the top meetings last week between Biden and Starmer. 

Reuters contributed to this report.