BEIRUT (AP) -- Syria's state news agency says a massive explosion that tore through a residential area and killed at least 16 people in the city of Hama was caused by anti-regime bomb-makers who mishandled explosives.
The Syrian Observatory for Human Rights, an activist group, said it is not sure what set off Wednesday's explosion and asked U.N. monitors to investigate.
The Observatory had initially cited witnesses as saying the blast on Hama's outskirts was caused by government shelling. Another activist group, the Local Coordination Committees, also blamed the regime and said dozens were killed.
Amateur video posted online showed a ball of fire and smoke rising from the neighborhood and residents searching the rubble. The Observatory said Thursday that at least 16 were killed.