It's the second large weapons seizure in the region this month, and both may have been headed to Yemen from Iran.
According to a U.S. assessment, the arms recently seized originated in Iran, and their likely destination was Yemen
, Cmdr. Kevin Stephens, a spokesman for the U.S. Navy's 5th Fleet, told CNN.
French authorities released the crew of 10 after questioning them, according to the French Defense Ministry.
Iran has been accused of arming Houthis -- fellow Shiite Muslims fighting against the government in Yemen's civil war. Stephens would not specify whether or not the United States believed the weapons shipment was headed to Houthi rebels.
Earlier this month,
an Australian naval ship discovered a similar arms cache off Oman. U.S. authorities said those weapons were believed to be initially sent from Iran and were probably intended for Houthi rebels in Yemen by way of Somalia, according to Lt. Ian McConnaughey with the U.S. Navy.
The March 20 discovery is the third such weapons seizure since September, Stephens said.
French forces spotted the ship carrying the arms as part of routine surveillance in the northern Indian Ocean.
On board the vessel, they found "several hundred AK47 assault rifles, machine guns and anti-tank weapons," according to a statement Monday from the Combined Maritime Forces.
The CMF is a multinational naval partnership -- which includes France -- that helps police more than 3 million square miles of international waters.
"France has been supporting Combined Maritime Forces operations since their inception," the CMF said.
The CMF routinely conducts boardings to determine the origin of unmarked vessels (so-called flag verification boardings) on a regular basis, McConnaughey said. That led to the March 7 discovery of weapons.
The proxy fight
This latest weapons seizure would provide another example of forces inside Iran
stoking sectarian tensions in the Middle East if the U.S. assessment proves correct.
For years, the Houthis have held sway in northern Yemen but lacked influence in the country's Sunni-led government.
Yemen's civil war is largely seen as a proxy fight between Iran and Saudi Arabia
, with Yemeni President Abdu Rabu Mansour Hadi backed by the Saudis
and other Sunni Gulf states.
The Houthi rebels seized Yemen's presidential palace in January 2015, temporarily forcing Hadi from Sanaa, the capital.
He later returned in large part with the help of airstrikes from Saudi Arabia, the United Arab Emirates, Kuwait, Bahrain, Qatar and others that joined to battle the Houthis.