White Helmets rescuers at the scene of an explosion in Jisr al-Shughour in northwest Syria, April 24, 2019

Assad regime shelling has killed at least seven civilians, and possibly as many as 25, in opposition-held northwest Syria since Tuesday.

The seven confirmed fatalities, including four children, from regime attacks were in Khan Sheikhoun in southeast Idlib Province on Tuesday. Eighteen people were slain on Wednesday by an explosion near a market in Jose al-Shughour in northwest Idlib, but reports conflicted over whether the cause was rockets or a car bomb.

Local sources said the regime barrage continued on Wednesday in Khan Sheikhoun —- the site of a regime sarin attack in April 2017 that killed about 90 people and wounded hundreds —- and on Saraqeb, causing casualties in both locations.

The blast in Jisr al-Shughour levelled a four-story building and damaged nearby structures to the point of collapse.

The regime has regularly defied a demilitarized zone, announced by Russia and Turkey last September. The shelling has escalated since mid-February, with at least 142 people killed and tens of thousands displaced.

Despite its declaration of the demilitarized zone, Russia has occasionally carried out airstrikes on Idlib, on the pretext that it is targeting “terrorists”.

The hardline bloc Hayat Tahrir al-Sham (HTS) group, which has claimed retaliation for the shelling, said it killed 10 regime troops in the village of Hakoura in northern Hama Province on Tuesday.

Russia, Turkey, and Iran convene on Thursday for another round of political talks in the Kazakh capital Astana.

Turkey has had forces alongside rebels in the northwest since August 2016, when it intervened to push out the Islamic State and then to take much of the Kurdish canton of Afrin.

Iran has supported the Assad regime’s desire to recapture the northwest, although it has been muted on the issue in recent months.