A police trooper stands on an armoured personnel carrier positioned at a checkpoint in Sanaa March 8, 2015. Yemen's defence minister has fled Houthi-controlled Sanaa for Aden, officials said on Sunday, in a move expected to bolster President Abd-Rabbu Mansour Hadi in his power struggle with the Shi'ite Muslim group. REUTERS/Mohamed al-Sayaghi (YEMEN - Tags: POLITICS CIVIL UNREST MILITARY)