Vehicles burn after an explosion at central Damascus February 21, 2013, in this handout photograph released by Syria's national news agency SANA. The big explosion shook the central Damascus district of Mazraa on Thursday, residents said, and Syrian state media blamed what it said was a suicide bombing on terrorists battling President Bashar al-Assad. Syrian television broadcast footage of at least four bodies strewn along a main street and firefighters dousing the charred remains of dozens of burning vehicles. Black smoke billowed into the sky. REUTERS/Sana (SYRIA - Tags: CONFLICT POLITICS) ATTENTION EDITORS - THIS PICTURE WAS PROVIDED BY A THIRD PARTY. REUTERS IS UNABLE TO INDEPENDENTLY VERIFY THE AUTHENTICITY, CONTENT, LOCATION OR DATE OF THIS IMAGE. FOR EDITORIAL USE ONLY. NOT FOR SALE FOR MARKETING OR ADVERTISING CAMPAIGNS. THIS PICTURE IS DISTRIBUTED EXACTLY AS RECEIVED BY REUTERS, AS A SERVICE TO CLIENTS