Air force troopers and policemen gather at the site of a bomb attack on a military bus in Sanaa August 25, 2013. At least six people were killed and 26 others injured on Sunday in a bomb attack on a bus carrying members of Yemen’s air force to their base in the capital Sanaa, witnesses and medics said. REUTERS/Khaled Abdullah (YEMEN – Tags: POLITICS CIVIL UNREST MILITARY)