A missile attack by Yemen's Houthi rebels on a commercial ship in the Gulf of Aden on Wednesday killed three of its crew members and forced survivors to abandon the vessel, the U.S. military said. It was the first fatal strike in a campaign of assaults by the Iranian-backed group over Israel's war on Hamas in the Gaza Strip.

The attack on the Barbados-flagged, Liberian-owned bulk carrier True Confidence further escalates the conflict on a crucial maritime route linking Asia and the Middle East to Europe that has disrupted global shipping. The Houthis have launched attacks since November, and the U.S. began an airstrike campaign in January that so far hasn't halted their attacks.

Meanwhile, Iran announced Wednesday that it would confiscate a $50 million cargo of Kuwaiti crude oil for American energy firm Chevron Corp. aboard a tanker it seized nearly a year earlier. It is the latest twist in a yearslong shadow war playing out in the Middle East’s waterways even before the Houthi attacks began.

The U.S. military's Central Command said an anti-ship ballistic missile launched from a Houthi-controlled area in Yemen struck the True Confidence, causing significant damage to the ship. In addition to the three deaths, at least four crew members were injured, with three in critical condition.

The attack came after the ship had been hailed over radio by men claiming to be the Yemeni military, officials said. The Houthis have been hailing ships over the radio in the Red Sea and the Gulf of Aden since beginning their attacks, with analysts suspecting the rebels want to seize the vessels.

After the missile hit, the crew abandoned the ship and deployed lifeboats. A U.S. warship and the Indian navy were on the scene, trying to assist in rescue efforts. It was unclear how many crew members were on board at the time.

The United Nations called on the Houthis “to cease all attacks against international shipping in the Red Sea,” U.N. spokesman Stephane Dujarric said, expressing serious concern about the continuing attacks, including the latest incident where the status of the crew is unknown.

Dujarric said the attacks are causing risks “to property, to life, to ecology in the area.”

At the State Department in Washington, spokesman Matthew Miller condemned the attack. “We continue to watch these reckless attacks with no regard for the well being of innocent civilians who are transiting through the Red Sea. And now they have, unfortunately and tragically, killed innocent civilians,” he told reporters.

Brig. Gen. Yahya Saree, a Houthi military spokesman, claimed the attack in a prerecorded message, saying its missile fire set the vessel ablaze. He said the rebels' attacks would only stop when the “siege on the Palestinian people in the Gaza is lifted.”

The rebels have repeatedly targeted ships in the Red Sea and surrounding waters over the Israel-Hamas war, but up to Wednesday hadn't killed any crew members. The vessels have included at least one with cargo bound for Iran, the Houthis’ main benefactor, and an aid ship later bound for Houthi-controlled territory.

Despite more than a month and a half of U.S.-led airstrikes, Houthi rebels have remained capable of launching significant attacks. They include the attack last month on a cargo ship carrying fertilizer, the Rubymar, which sank on Saturday after drifting for several days, and the downing of an American drone worth tens of millions of dollars.

It was unclear why the Houthis targeted the True Confidence. However, it had previously been owned by Oaktree Capital Management, a Los Angeles-based fund that finances vessels on installments. Oaktree declined to comment.

Meanwhile, a separate Houthi assault Tuesday apparently targeted the USS Carney, an Arleigh Burke-class destroyer that has been involved in the American campaign against the rebels. The Carney shot down bomb-carrying drones and one anti-ship ballistic missile, the Central Command said. Saree acknowledged that attack as well.

The U.S. later launched an airstrike destroying three anti-ship missiles and three bomb-carrying drone boats, the Central Command said.

The Houthis haven't offered any assessment of the damage they've suffered in the American-led strikes that began in January, though they've said at least 22 of their fighters have been killed. One civilian has reportedly been killed.

The U.S. Treasury separately announced new sanctions targeting a Houthi financier and the expeditionary Quds Force of Iran's paramilitary Revolutionary Guard, which arms the rebels.

The Houthis have held Yemen's capital, Sanaa, since 2014. They've battled a Saudi-led coalition since 2015 in a long-stalemated war there.