The Houthis' military spokesman confirmed the seizure of a cargo ship but said it was carrying military equipment and engaged in "hostile acts targeting the security and stability of the Yemeni people".
The ship was heading to the Saudi port of Jizan, just north of Yemen, from the Yemeni Red Sea island of Socotra when it was attacked just before midnight on Sunday, Saudi state news agency SPA reported, quoting coalition spokesman Brigadier General Turki al-Malki.
It was carrying equipment from a shuttered field hospital, when it was attacked, SPA said.
Saudi Arabia is leading a military coalition that has been battling the Houthis for more than six years.
The alliance has accused the movement of attacking shipping in the Red Sea, one of the world's busiest maritime lanes leading to the Suez Canal.
The United Kingdom Maritime Trade Operations (UKMTO) said late on Sunday it had received reports of an attack on a vessel near Yemen's port of Ras Isa, which lies slightly north of Hodeidah, and an investigation was under way.
It was not immediately clear if it was the same attack.
In an advisory issued on Monday, UKMTO, part of Britain's Royal Navy, advised mariners to exercise extreme caution in the area.
