Yemen's Iran-aligned Houthi militants launched a projectile into southern Saudi Arabia that landed near a desalination plant but did not cause any damage or casualties.
The Saudi-led coalition fighting the rebels said the projectile launched late Wednesday struck near the plant in the Al-Shuqaiq area of Jizan.
Coalition spokesman Turki al-Maliki said the group would take "firm measures, urgent and timely, to deter this terrorist militia."
The Houthis, who ousted the Saudi-backed internationally recognized government from power in the Yemeni capital, Sanaa, in late 2014, have stepped up missile and drone attacks on Saudi cities in the past two weeks.
Last week, a rebel missile hit an international airport in Abha, Saudi Arabia, wounding 26 people.
In Washington, White House spokeswoman Sarah Sanders said U.S. President Donald Trump had been briefed on the strike.
Pentagon spokeswoman Navy Cmdr. Rebecca Rebarich said such attacks were "a significant cause for concern and [put] innocent lives at risk."