Iran-backed Houthis, who say their attacks are in support of Palestinians under siege by Israel in Gaza, have targeted commercial shipping in the Red Sea.
The United States on Friday accused Iran of close involvement in attacks on commercial ships by Yemen's Huthi rebels, alleging Tehran's clerical state has provided drones, missiles and tactical intelligence.
The allegations, released by the White House based on US intelligence, mark the strongest remarks yet by the United States on Iran's purported role in the attacks.
"We know that Iran was deeply involved in planning the operations against commercial vessels in the Red Sea," National Security Council spokeswoman Adrienne Watson said.
"This is consistent with Iran's long-term materiel support and encouragement of the Huthis' destabilizing actions in the region," she said.
"We have no reason to believe that Iran is trying to dissuade the Houthis from this reckless behavior," she said.
The Iran-backed Huthis have repeatedly targeted vessels in the vital shipping lane with strikes they say are in support of Palestinians in Gaza, where Israel is battling militant group Hamas.
The United States and its allies have worked to intercept the attacks and the Pentagon recently announced a coalition of more than 20 countries to protect Red Sea shipping.