A Syrian or Russian air strike was reported to have killed at least 19 people and possibly many more at a market in northwestern Syria on Monday, straining a cessation of hostilities agreement meant to pave the way for peace talks.

In a further upsurge in violence, al Qaeda’s Nusra Front and other Islamist insurgents not included in the U.S.-Russian agreement attacked government forces in a neighboring province, taking over a village and at least two hilltops in their first advance for some time in the area, a monitoring group said.

The agreement, accepted by President Bashar al-Assad’s government and most of his enemies, has reduced violence in Syria since it took effect on Feb 27, the first truce of its kind in a 5-year-old war that has killed more than 250,000 people and caused the world’s worst refugee crisis. […]