Those being evacuated are the last American troops stationed in the Arab nation, which is home to al Qaeda in the Arabian Peninsula, the terrorist group also known as AQAP. The United States closed its embassy in Sanaalast month, after Houthi rebels took over the Yemeni capital. And hundreds of al Qaeda members escaped two Yemeni prisons Thursday and Friday, raising further security questions.

For years, the U.S. military has worked closely with Yemen's government to go after AQAP, together carrying out numerous attacks like the 2011 drone strike that killed prominent al Qaeda figure Anwar al-Awlaki. And U.S. President Barack Obama has hailed this cooperation as a pillar in his anti-terrorism campaign.

"Yemen has never been a perfect democracy or a island of stability," Obama said in January, promoting the policy of "partnering and intelligence-sharing with that local government" as the best approach in a bad situation.

"The alternative would be for us to play whack-a-mole every time there is a terrorist actor inside of any given country," the President said.