Drone and rocket attacks on cargo ships in the Red Sea have now prompted US and UK-led forces to stage air strikes on targets in the region.
US President Joe Biden said the US and UK military had successfully launched strikes early on Friday against Houthi targets with support from Australia, Bahrain, Canada and the Netherlands.
The Houthi targets in Yemen included logistical hubs, air defence systems and arms depots.
Why have the Houthis attacked Red Sea ships?
The attacks began after the start of the Israel-Hamas war on 7 October.
The Houthis declared their support for Hamas and said they would target any ship travelling to Israel. It is not clear that all of the ships attacked were actually heading there.
In November they seized what they said was an Israeli cargo ship.
Houthi attacks in the Red Sea have increased 500% between November and December.
Major shipping firms including Mediterranean Shipping Company, Maersk, Hapag-Lloyd and the oil company BP have all said they are diverting vessels away from the Red Sea.