Policemen look at the wreckage of a car at the scene of a car bomb outside the police college in Sanaa January 7, 2015. A car bomb exploded outside a police college in Yemen's capital Sanaa early on Wednesday, killing around 30 people and wounding more than 50 others, police sources and residents said. REUTERS/Khaled Abdullah

Police investigators look at the wreckage of a car at the scene of a car bomb outside the police college in Sanaa January 7, 2015. A car bomb exploded outside a police college in Yemen's capital Sanaa early on Wednesday, killing around 30 people and wounding more than 50 others, police sources and residents said. REUTERS/Khaled Abdullah

Policemen gather at the scene of a car bomb outside the police college in Sanaa January 7, 2015. A car bomb exploded outside a police college in Yemen's capital Sanaa early on Wednesday, killing around 30 people and wounding more than 50 others, police sources and residents said. REUTERS/Khaled Abdullah

A policeman walks past a wreckage at the scene of a car bomb outside the police college in Sanaa January 7, 2015. A car bomb exploded outside a police college in Yemen's capital Sanaa early on Wednesday, killing around 30 people and wounding more than 50 others, police sources and residents said. REUTERS/Khaled Abdullah

A police investigator looks at a damaged car at the scene of a car bomb outside the police college in Sanaa January 7, 2015. A car bomb exploded outside a police college in Yemen's capital Sanaa early on Wednesday, killing around 30 people and wounding more than 50 others, police sources and residents said. REUTERS/Khaled Abdullah

Policemen look at the wreckage of a car at the scene of a car bomb outside the police college in Sanaa January 7, 2015. A car bomb exploded outside a police college in Yemen's capital Sanaa early on Wednesday, killing around 30 people and wounding more than 50 others, police sources and residents said. REUTERS/Khaled Abdullah