By Levent Tok, Burak Karacaoglu

IDLIB, Syria

At least six people were killed in a series of blasts that hit the opposition-held Idlib city in northwestern Syria on Wednesday, a pro-opposition Syrian civil defense official said.

Mohamed Hajj Yusuf, head of Syrian civil defense in Idlib, told Anadolu Agency that one person was also critically injured in the explosions that took place in the central part of the city.

Yusuf added that cause of the blasts remains unknown.

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.

The conflict escalated in 2014 after Daesh overran vast swathes of territory in both Syria and Iraq, where -- despite a string of recent losses -- it still maintains a significant presence.