The transfer, announced last week, comes at a time when Ukraine is facing ammunition shortages and Republican lawmakers in the US are blocking new aid. 

The shipment does not include supplies to meet Kiev's need for important items such as artillery and air defense ammunition. 

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"The U.S. government has transferred more than 5,000 AK-47 machine guns, sniper rifles, RPG-7s and more than 500,000 rounds of 7.62mm ammunition to the Ukrainian Armed Forces. These weapons will contribute to Ukraine's defense against the Russian invasion. There is enough material to equip a brigade."

The weapons and ammunition were intercepted on four "stateless vessels" between May 2021 and February 2023 while being transferred from the Iranian Revolutionary Guard Corps to Houthi rebels in Yemen, CENTCOM said.

The term "stateless vessel" is used for ships that sail in international waters but do not fly the flag of any country. 

"The government acquired ownership of these munitions on December 1, 2023, through a confiscation order by the Ministry of Justice," the statement continued. 

Since November 2023, the Iranian-backed Shiite rebel Houthi movement, which controls key cities in Yemen, including the capital Sana'a, has been carrying out attacks on ships sailing in the Red Sea in solidarity with Palestinians in Gaza, which is under Israeli aggression. 

Houthi attacks target ships in the Red Sea and Gulf of Aden. These attacks are seen as a major 'international security challenge' that threatens maritime shipping lanes. 

Congress deadlock over aid to Ukraine

"Iran's support for armed groups threatens international and regional security, our forces, diplomatic personnel, citizens and partners in the region," the US Central Command statement added. We will continue to do all we can to illuminate and stop Iran's destabilizing activities."

In October, Washington announced a similar shipment to Ukraine, saying that 1.1 million rounds of ammunition seized from Iranian-backed forces en route to Yemen had been sent to Ukraine. 

However, the delivery of key artillery and air defense ammunition to Ukraine has been blocked by Republican lawmakers in the US Congress who have stalled a $60 billion aid package since last year.