US B-2 bombers attacked weapons depots belonging to Houthi rebels in Yemen.

Defense Secretary Lloyd Austin said the operation was ordered late Wednesday by President Joe Biden to "further degrade" the Houthis' ability to launch attacks on commercial and military ships in the Red Sea.

The attacks could also be a warning to Iran at a time when Tehran and US ally Israel appear on the brink of all-out war.

Austin did not mention Iran by name, but he said the use of the B-2 bomber, which is the only fighter jet in the US arsenal that can carry so-called bunker-busting bombs.

"It was a unique demonstration of the ability of the US to target facilities that our adversaries are trying to hold, regardless of whether they are deep underground or fortified," he said.

The top US defense official said the "precision strikes" targeted five underground weapons storage sites in Houthi-controlled areas of Yemen. There were no immediate reports of casualties, the military said.

In Yemen, the Houthis have sporadically attacked ships in the Red Sea, a major trade route, for years, but attacks against civilian tankers and cargo ships have intensified since the conflict between Israel and Hamas began last year.

The Houthis say their attacks are a sign of solidarity with Hamas, which is also supported financially and with weapons by Iran, and Palestinians in general.

Increased rebel attacks have prompted an increasing number of US-led strikes against Houthi targets, including radars, airstrips, missile launch sites and logistics hubs.

US forces have also shot down Houthi attack drones and missiles targeting Israel. /USAToday