The British military launched airstrikes with the United States targeting Yemen’s Houthi rebels. The strikes Tuesday night marked their first involvement with America’s new intense campaign targeting the Iranian-backed group.

Yemen’s Houthi rebels alleged on Monday that a US airstrike hit a prison holding African migrants. The US military had no immediate comment.

American forces have hit more than 1,000 Houthi targets in Yemen as part of a campaign that began in March to stop attacks by the militants on the shipping lanes of the Red Sea, the Pentagon said Tuesday.