The Houthis have attacked civilian and military ships sailing off Yemen's shores at least 50 times since their assaults began late last year, a senior US Defense Department official said Thursday.

"In the Red Sea, the Houthis seek to affect this vital channel for global trade with at least 50 attacks against commercial shipping and naval vessels," Assistant Secretary of Defense Celeste Wallander told a House Armed Services Committee hearing.

The Houthis began attacking ships in November, a campaign they say is intended to signal solidarity with Palestinians in Gaza.

They have vowed to target Israeli, British and American ships, as well as vessels heading to Israeli ports, disrupting traffic through the vital trade route off Yemen's coasts.

The attacks have sent insurance costs spiraling for vessels transiting the Red Sea and prompted many shipping firms to take the far longer passage around the southern tip of Africa instead.

The US and Britain have since January carried out strikes targeting the Houthis, but the military officer responsible for US forces in the Middle East said Houthi equipment that has been destroyed can be replaced with relative ease.

"Only two ships can resupply the vast majority of the equipment that we've destroyed so far of the Houthis," General Erik Kurilla told the same hearing, without specifying the size of the vessels.

"We have to increase the international effort to be able to do the inspections on the vessels that are going into Hodeidah," he said, referring to a Houthi-contolled Yemeni port, adding: "We need to isolate the Houthis in the information environment, and we have to impose costs on Iran."