Yemen's Houthi movement will expand its targets in the Red Sea region to include U.S. ships, an official from the Iran-allied group said on Monday, as it vowed to keep up attacks after U.S. and British strikes on its sites in Yemen.

Attacks by the Houthis on ships in the area since November have impacted companies and alarmed major powers in an escalation of Israel's more than three-month war with Hamas militants in the Gaza Strip. The group says it is acting in solidarity with Palestinians.

British and American ships had become "legitimate targets" due to the strikes launched by the two countries on Yemen last week, Nasruldeen Amer, a spokesperson for the Houthis, told Al Jazeera.