Newly recruited fighters parade outside the U.S. embassy before they join Houthi rebels in the battles frontline at the border with Saudi Arabia and in other parts of Yemen, in the capital Sanaa, Yemen July 17, 2017.

Newly recruited fighters parade outside the U.S. embassy before they join Houthi rebels in the battles frontline at the border with Saudi Arabia and in other parts of Yemen, in the capital Sanaa, Yemen July 17, 2017.

Newly recruited fighters parade outside the U.S. embassy before they join Houthi rebels in the battles at the border with Saudi Arabia and in other parts of Yemen, in the capital Sanaa, Yemen July 17, 2017.

A newly recruited fighter holds a poster of the Houthi movement's founder Hussein Badruddin al-Houthi as he parades with comrades outside the U.S. embassy before they join Houthi rebels in the battles frontline at the border with Saudi Arabia and in other parts of Yemen, in the capital Sanaa, Yemen July 17, 2017.

Newly recruited fighters parade outside the U.S. embassy before they join Houthi rebels in the battles frontline at the border with Saudi Arabia and in other parts of Yemen, in the capital Sanaa, Yemen July 17, 2017. Reuters/ Khaled Abdullah

Newly recruited fighters parade outside the U.S. embassy before they join Houthi rebels in the battles frontline at the border with Saudi Arabia and in other parts of Yemen, in the capital Sanaa, Yemen July 17, 2017. The shoulder badge reads: "Allah is the greatest. Death to America, death to Israel, a curse on the Jews, victory to Islam".

A newly recruited fighter holds a poster of the Houthi movement's leader Abdulmalik al-Houthi, as he parades with comrades outside the U.S. embassy before they join Houthi rebels in the battles frontline at the border with Saudi Arabia and in other parts of Yemen, in the capital Sanaa, Yemen July 17, 2017.

Newly recruited fighters ride on the back of a patrol truck as they parade outside the U.S. embassy before they join Houthi rebels in the battles frontline at the border with Saudi Arabia and in other parts of Yemen, in the capital Sanaa, Yemen July 17, 2017.

Newly recruited fighters parade outside the U.S. embassy before they join Houthi rebels in the battles frontline at the border with Saudi Arabia and in other parts of Yemen, in the capital Sanaa, Yemen July 17, 2017. The placards read, "Allah is the greatest. Death to America, death to Israel, a curse on the Jews, victory to Islam".

Newly recruited fighters parade outside the U.S. embassy before they join Houthi rebels in the battles frontline at the border with Saudi Arabia and in other parts of Yemen, in the capital Sanaa, Yemen July 17, 2017. The placard reads, "Allah is the greatest. Death to America, death to Israel, a curse on the Jews, victory to Islam".

Newly recruited fighters parade outside the U.S. embassy before they join Houthi rebels in the battles at the border with Saudi Arabia and in other parts of Yemen, in the capital Sanaa, Yemen July 17, 2017.