A blast at a munitions depot in Syria's northwestern Idlib region killed three people, including a woman, said the Syrian Observatory for Human Rights.
The explosion completely destroyed the warehouse and caused a fire in a nearby camp, an AFP correspondent who reached the scene near the town of Fuaa reported.
The blast destroyed "a warehouse run by extremist militants and where missiles and explosive devices were manufactured," said Observatory chief Rami Abdulrahman.
According to the monitor’s sources, the explosion killed two fighters and a woman who lived nearby, while six people from the camp were wounded.
Reports have suggested that the explosion was caused by an air strike, but the perpetrator is still unknown.
Despite a ceasefire in Idlib and neighboring regions, Russian aircraft still carry out airstrikes targeting the Hayat Tahrir Al Sham (HTS) and other extremist factions.
American warplanes also target extremist positions, especially al-Qaeda-linked groups in the region.
The Observatory could not immediately specify which organization ran the warehouse, but said it was not held by the HTS.
The HTS has weeded out rivals from much of the area, but small factions remain.