The Navy disclosed Monday that it recently confiscated a weapons cache from a small fishing craft in the Arabian Sea, seizing about 1,500 Kalashnikov rifles, 200 rocket-propelled grenade launchers and 21 .50-caliber machine guns. It marks the fourth seizure by a U.S.-led maritime task force in the region since September — and underscores the difficulties the United States faces in stopping weapons smuggling to nations like Yemen, where Houthi rebels continue to rely on Iranian arms.

The weapons commonly move on a small craft known as a dhow, a traditional sailing vessel in the Middle East. Foreign policy and military experts said the smuggling has occurred for years, but it comes now at a sensitive time in which the Obama administration is trying to manage the nuclear agreement it reached last year with Iran. International economic sanctions against Tehran were lifted this year as part of the deal in exchange for Iran sending the bulk of its enriched uranium out of the country, disabling one nuclear reactor and shelving the majority of its centrifuges.

Iran has continued a variety of other actions in the Middle East that the United States considers destabilizing. While the U.S.-led coalition has confiscated several shipments of weapons, there’s no way of knowing how many boats have made it through to Yemen, said Michael Knights, a fellow with the Washington Institute, a think tank focused on Middle Eastern issues. The U.S. military is “stuck in the middle” as the United States does “this kind of dance between two extremes” inside Iran. […]