Yemen's Huthi rebels have attacked international shipping and fired on U.S. naval forces in the Red Sea for over a year.
The Huthis' missile and drone attacks have disrupted a key global trade route and triggered retaliatory strikes by the United States and Britain.
Now, U.S. media reports suggest that Russia has been helping the rebels pick their targets -- most of them commercial ships owned or operated by Western companies or vessels heading to or coming from Israel.
Experts say Russia is expanding its cooperation with the Huthis, a U.S.-designated terrorist organization that is backed by Iran, including by sharing intelligence.
Moscow could even supply the Huthis with advanced arms in response to Washington loosening restrictions on Ukraine's use of U.S.-supplied weapons.
"It sends a message to the United States that Russia could make life very painful if it wants to, and it's a not-so-veiled threat that could be construed as retaliation for Washington's assistance to Ukraine," said Colin Clarke, director of policy and research at the New York-based Soufan Group intelligence consultancy.
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Who Are The Huthi Rebels And What Are Their Links To Iran?
Enemy Of My Enemy
The Huthis have said their attacks on Western and Israeli targets in the Red Sea are in response to Israel's devastating yearlong war in the Gaza Strip.
The rebels have vowed to continue their attacks, which include direct missile and drone attacks on Israel, until a cease-fire is reached in the Palestinian enclave.
The Gaza war has pitted Israel against Iran's so-called axis of resistance, a loose network of state and nonstate actors that include the Huthis, Hamas, Hezbollah, and Shi'ite militias in Iraq and Syria.
Experts say Russia's support for the Huthis aligns with the Kremlin's narratives about opposing the West and empowering anti-Western armed groups globally.
"The Kremlin is interested in having friends who can test the nerves of Moscow's enemies in the Red Sea or anywhere in the Middle East," Ruslan Suleymanov, an academic and oriental studies expert, told Current Time.
He added Russia also wants to be seen supporting any group that "stands up to the West."
Fires burn aboard the oil tanker Sounion in the Red Sea after it was struck by the Huthis on August 25.
U.S. media reports and intelligence in recent months suggest that Russia is providing intelligence, including satellite data, to the Huthis to attack commercial ships in the Red Sea.
Since July, reports have said the Kremlin even threatened to transfer anti-ship missiles to the Huthis, but that the United States and Saudi Arabia dissuaded Russia.
Experts say that could change after Washington on November 17 reportedly allowed Ukraine to use longer-range U.S. Army Tactical Missile Systems (ATACMS) to strike inside Russia.
"The Russian consideration of arming the Huthis has been directly related to what [Russian President] Vladimir Putin perceives as U.S. escalation against Russia in progressively loosening restrictions on Ukraine's use of U.S.-supplied weaponry," said Kenneth Katzman, former senior Middle East analyst for the U.S. Congress.
In addition to disrupting shipping in the Red Sea, Russia is reportedly using the Huthis to recruit fighters from Yemen to join the war against Ukraine. Moscow is also ensuring that Russian ships can safely transit the Red Sea.
The Huthis have wrested control of Yemen's northwest and Red Sea coastline since the country's devastating civil war erupted in 2014.
Boon For The Huthis
Experts say the Huthis stand to gain by expanding their relations with Russia.
Clarke of the Soufan Group said Russian intelligence helped the rebels more accurately target Western vessels in the Red Sea. It also shows that the Huthis are not an "uncontrollable gang of terrorists," he said.
"On the contrary, they are a rational actor, a highly capable organization that is becoming an even bigger player in the Middle East and doing so through asymmetric means," Clarke added.
Russian President Vladimir Putin (left) meets with Iranian Supreme Leader Ayatollah Ali Khamenei in Tehran in November 2017.
Iran is the Huthis' main military backer, supplying them with weapons technology and missile components, according to U.S. intelligence.
Experts say the rebels would benefit significantly from Russian missile technology, which Katzman said was "far more precise and effective" than the arms provided by Tehran.
This could lessen the group's dependence on Iran, an ally of Russia.
"The Russian weaponry might even enable the Huthis to successfully strike U.S. and coalition warships, which could escalate the Red Sea conflict enormously, were the Huthis to actually strike a U.S. naval vessel," Katzman said.