Washington DC - Attacks by Houthi rebels in Yemen have forced three-fourths of US-flagged ships to avoid the Red Sea and instead take the long and expensive detour around the southern tip of Africa, the US national security advisor said Sunday.

"75% of our US flag shipping now has to go around the southern coast of Africa rather than going through the Suez Canal," Mike Waltz told CBS's Face the Nation.

He added: "The last time one of our destroyers went through the straits there, it was attacked 23 times."

Recent US airstrikes against the Iran-backed rebels – the first since President Donald Trump took office in January – have "taken out key Houthi leadership," including the head of their missile program, Waltz said.

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"We've hit their headquarters. We've hit communications nodes, weapons factories, and even some of their over-the-water drone production facilities."

The Houthis say they have targeted ships in the Red Sea in solidarity with Palestinians since the start of the Gaza war. They say the recent US bombing attacks on Yemen claimed more than 50 lives.

On Tuesday, they said on Telegram that they had fired missiles and drones at the aircraft carrier USS Harry S Truman, part of the US fleet in the northern Red Sea. Those attacks were unsuccessful, NBC reported.

Waltz blamed the administration of Joe Biden for launching only "pinprick attacks" against the Houthi, allowing "one of the world's most critical sea lanes [to] get shut down."

He added: "The Trump administration and President Trump have decided to do something much harder, much tougher."

Traveling around the southern tip of Africa can double the time it takes a ship to pass between Europe and Asia, adding nearly $1 million in costs, according to LSEG Shipping Research.