U.S. President Donald Trump says he has ordered airstrikes against Iran-backed rebels in Yemen, and issued a warning to Tehran.

Here’s why.

Threat to global shipping

The Houthi rebels started attacking military and commercial ships on one of the world’s busiest shipping corridors shortly after the war in Gaza began between Hamas and Israel in October 2023.

The Houthis said they were targeting vessels on the Red Sea with links to Israel or its allies — the United States and the U.K. — in solidarity with Palestinians, but some vessels had little or no link to the war.

The Houthis targeted over 100 merchant vessels with missiles and drones, sinking two vessels and killing four sailors, until the current ceasefire in Gaza took effect in mid-January. Other missiles and drones were intercepted or failed to reach their targets, which included Western military ones.

The attacks paused during the ceasefire, but the Houthis on Wednesday said they would resume against “any Israeli vessel” after Israel cut off all aid supplies to Gaza to pressure Hamas during talks on extending their truce. The rebels said the warning also affects the Gulf of Aden, the Bab el-Mandeb Strait and the Arabian Sea.

No Houthi attacks have been reported since then.

“These relentless assaults have cost the U.S. and World Economy many BILLIONS of Dollars while, at the same time, putting innocent lives at risk,” Trump said Saturday while announcing the airstrikes in a social media post.

Threat to the U.S.

The earlier Houthi campaign saw U.S. and other Western warships repeatedly targeted, sparking the most serious combat the U.S. Navy had seen since World War II.

The United States under the Biden administration, as well as Israel and Britain, previously struck Houthi-held areas in Yemen. But a U.S. official said Saturday’s operation was conducted solely by the U.S.

The USS Harry S. Truman carrier strike group, which includes the carrier, three Navy destroyers and one cruiser, are in the Red Sea and were part of Saturday’s mission. The USS Georgia cruise missile submarine has also been operating in the region.

Trump said the strikes were to “protect American shipping, air, and naval assets, and to restore Navigational Freedom.”

The focus on the Houthis and their attacks have raised their profile as they face economic and other pressures at home amid Yemen’s decadelong stalemated war, which has torn apart the Arab world’s poorest nation.

Pressure on Iran

Saturday’s strikes also were meant to pressure Iran, which has backed the Houthis just as it has supported Hamas and other proxies in the Middle East.

Trump vowed to hold Iran “fully accountable” for the Houthis’ actions.

The State Department earlier this month reinstated the “foreign terrorist organization” designation for the Houthis, which carries sanctions and penalties for anyone providing “material support” for the group.

The Trump administration also has been pressing Iran to restart bilateral talks on Iran’s advancing nuclear weapons program, with Trump writing a letter to the country’s supreme leader. Trump, who unilaterally withdrew America from Iran’s 2015 nuclear deal with world powers, has said he will not allow the program to become operational.

Iran has insisted that its nuclear program is peaceful. However, its officials increasingly threaten to pursue a nuclear weapon.

Trump has also levied new sanctions on Iran as part of his “maximum pressure” campaign against the country and has suggested that military action remains a possibility, while emphasizing he still believes a new nuclear deal can be reached.

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Associated Press writer Lolita C. Baldor in Washington contributed.