An explosion in a residential area of Hama, Syria, killed at least 16 people and was caused by anti-regime bomb-makers mishandling explosives, the state news agency reported Thursday.
Reports varied, however, on how high the number of dead and injured may be.
Activists posted video on the web showing a scene of devastation, with bodies being pulled from the rubble, one of them apparently a child. Another report said 13 children and 15 women were among the dead.
The level of devastation seen would have been difficult to achieve by conventional shelling, the BBC reported from Beirut, based on video evidence. State television showed pictures of injured children in hospital.
Some said the blast may have been caused by government forces shelling the area, or perhaps even a Scud missile attack.
The Syrian Observatory for Human Rights, an activist group, said it wasn't sure what set off Wednesday's explosion. It asked UN monitors now in the country to investigate.
Amateur video posted online showed a ball of fire and smoke rising from the neighbourhood and residents searching the rubble.
The Observatory put the death toll at 16. It had initially cited witnesses as saying the blast on Hama's outskirts was caused by government shelling. Another activist group, the Local Co-ordination Committees, also blamed the regime and said dozens of people were killed.