Iran has reportedly used the country's state-owned airline and boats to smuggle high-end drones to Russia for use in its war against Ukraine.

Sources within Iran told The Guardian reported that at least 18 advanced drones have been delivered to Russia's military since November, including six Mohajer-6 drones plus 12 Shahed 191 and 129 drones. Iran has also provided 54 technicians – about three per drone – to help the Russian military put the aircraft into service, according to the report.

While Iran previously shipped a significant number of single-use "kamikaze" drones to Russia that have been used against targets in Ukraine, the drones cited in the report are higher-end aircraft that can carry payloads and are designed to return to base after their mission – unlike the loitering munitions that are designed to be destroyed in the course of their mission.

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It's unclear exactly when the transfer of more advanced drones from Iran to Russia began, but the report noted that Ukrainian officials showed The Guardian a Mohajer-6 drone in November. Several had been downed by Ukraine's air defenses since September, the outlet reported.

According to the report, most of the more advanced drones were transferred from an Iranian vessel to a Russian navy boat in the Caspian Sea, while the others were moved by a state-owned Iranian airline. Iran and Russia both border the Caspian Sea, which would make it relatively easy for the two countries to transfer military hardware.

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The report comes a week after the U.S. imposed a new round of sanctions targeting Iran's drone industry. Those sanctions covered executives for the Paravar Pars Company, which produces unmanned aerial vehicles (UAVs) for Iran's military. Those include some of the Shahed "kamikaze" drones used by Russia in Ukraine. U.S. officials said that as of August about 1,000 of those single-use Iranian drones had been given to Russia

A recent report by Conflict Armament Research indicated that Iran has modified the warhead on some of the single-use Shahed drones provided to Russia to achieve maximum damage in multipurpose attacks, including those against civilian energy infrastructure and other targets.

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Iran's ties with Russia have deepened over the last year as western countries slapped sanctions on Russia's economy over the war in Ukraine.

The Middle Eastern country has sought a deal with the U.S. over Iran's nuclear program, as sanctions have taken a toll on its economy. However, Iran's crackdown on anti-regime protesters along with its support for Russia's war effort has dimmed the prospects for a new nuclear deal. 

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Despite U.S. sanctions that have been in place since America's withdrawal from the Iran nuclear deal in 2018, the Iranian energy sector ended 2022 on the upswing and its oil exports reached their highest level since 2019 amid strong demand from China and Venezuela.

Fox Business' Caitlin McFall contributed to this report.