By Halit Suleyman, Ayse Aktas

ANKARA/DARAA, Syria

Four civil defense workers died when a bomb exploded in Syria’s southwestern city of Daraa, a local civil defense official said Tuesday.

Ammar Ebu Zeyd told Anadolu Agency that four civil defense workers in an ambulance en route to the Nahta district, were killed in a roadside explosion.

The Daraa Civil Defense Center said in a statement that those who were targeted in the attack were headed to evacuate victims of a previous shelling.

Syria has been locked in a vicious civil war since early 2011 when the Assad regime cracked down on pro-democracy protests with unexpected ferocity.

Several rounds of peace talks -- in Geneva and the Kazakh capital Astana -- have so far failed to end the conflict, in which hundreds of thousands of Syrian civilians are believed to have been killed to date.