Why did Trump order airstrikes against rebels in Yemen?

Smoke rises from a location reportedly struck by US airstrikes in Sanaa, Yemen, on Saturday (Osamah Abdulrahman/AP)

The United States launched a wave of air strikes against Iran-backed rebels in Yemen as US President Donald Trump warned Tehran will be held “fully accountable” for their actions.

The Houthi-run health ministry said the strikes killed at least 31 people, including women and children, and injured more than 100.