The US military has launched cruise missile strikes to knock out three coastal radar sites in areas of Yemen controlled by Houthi rebel forces, in retaliation to missile attacks at its Navy ship.
Thursday's strikes, authorised by President Barack Obama, represent Washington's first direct military action against Houthi-controlled targets in Yemen's conflict.
Still, the Pentagon appeared to stress the defensive nature of the strikes, which were aimed at radars that enabled the launch of at least three missiles against the US Navy destroyer USS Mason since Sunday.
"These limited self-defence strikes were conducted to protect our personnel, our ships, and our freedom of navigation," Pentagon spokesman Peter Cook said.
US officials, speaking on condition of anonymity, said US Navy destroyer USS Nitze launched the Tomahawk cruise missiles around 4am local time (01:00 GMT), according to Reuters news agency.
"These radars were active during previous attacks and attempted attacks on ships in the Red Sea," including the USS Mason, one of the officials said, adding the sites were in remote areas where the risk of civilian casualties was low.
The official identified the areas in Yemen where the radars were targeted as near Ras Isa, north of Mukha and near Khoka.
The missile attacks on the USS Mason - the latest of which took place earlier on Wednesday - appeared to be the Houthis' response to a suspected Arab coalition strike on mourners gathered in Yemen's Houthi-held capital Sanaa.
The missile incidents, along with an October 1 strike on a vessel from the United Arab Emirates, add to questions about safety of passage for military ships around the Bab al-Mandab Strait, one of the world's busiest shipping routes.
The Pentagon warned against any future attacks.
"The United States will respond to any further threat to our ships and commercial traffic, as appropriate," Cook said.