Escalating violence in Syria in recent days has left a seven-week partial truce on the verge of collapse.
The latest incident piles pressure on the faltering Syrian peace talks in Geneva.
The air strikes in Idlib province are believed to be the deadliest since the cessation of hostilities took effect in February.
Two marketplaces in rebel-held towns in northwest Syria were hit.
Rescue workers say at least 38 people were killed when the central vegetable market in Maarat al-Numan was bombed at about noon.
Another ten people were killed in an air strike at another market in Kafranbel, about ten kilometres away.
At least three children are among the dead.
There was no immediate comment from the Syrian military, but US State Department spokesman John Kirby says it’s likely Assad government forces are reponsible for the attacks.
“It is our understanding at this time that it was most likely regime forces, but information is still coming in. So, I want to be a little careful here in how I couch that. And it has been, as we’ve said by and large, the majority of the violations have been by the regime. We have reason to believe at this point that that was the case with this particular bombing.”
Prospects for a speedy resumption of the UN-brokered Syrian peace talks in Geneva are fast diminishing.
Syrian opposition representatives have suspended their role in talks.
High Negotiations Committee spokesman Salim Al Muslat says the Idlib strikes are just the latest of many violations by the government of the partial truce.
“I believe we made the right decision now, because what’s going on there on the ground, what we’re having for the last few days is really a great deal of pressure from inside Syria because of the crimes that Assad is committing there. He did not respect the truce, the agreement by the Russian and the States. And now we witness the massacre in Maaret Al Numan in Idlib this really cannot be, if we look for successful political talks.”
Russia’s Foreign Minister, Sergei Lavrov, has been critical branding the decision a mistake.
Earlier, he said actors on the fringe of the conflict are to blame for disrupting peace talks.
“There are some players on the outside who still cherish the dream to overthrow the (Syrian) regime by force and try to do everything possible for that, including the attempts to provoke a failure of the Geneva talks.”
But Mr Lavrov says the decision to leave does not mean a complete breakdown of talks.
He says the opposition’s goal of a political settlement can only be achieved through negotiations.
But Syrian government delegates are resisting compromise too.
Syrian government chief negotiator Bashar Ja’afari says the political future of President al-Assad is not up for discussion.
“Our mandate as delegation engaged into the proximity talks in Geneva – stops and ends at forming the national unity government. We have no mandate whatsoever either to address the constitution, constitutional issue – meaning establishing the new constitution – or addressing the parliamentary elections, or addressing the fate of the presidency.”
He blamed what he called radicals in Turkey and Saudi Arabia for meddling in Syrian affairs and dooming the talks in Geneva.
“They don’t want to have, at the end of the day a political settlement, a peaceful political settlement to the Syrian crisis. 90 per cent of the Syrian crisis is mainly due to foreign hands, to foreign interference into Syrian domestic affairs.”
But other foreign influences are intent on ending the Syrian crisis by pushing peace talks – despite repeated setbacks.
White House spokesman Josh Earnest says the United Nations and the United States are determined to bring the warring parties back to the table.
“The UN, I would point out, has not described the situation as breaking down. They have acknowledged that the talks have been postponed but, you know, there still is a framework in place and I believe that there are still technical discussions that are taking place in Geneva even as we speak. So there still is a path forward here and it’s understandable that there is a frustration, to put it mildly, on the part of the opposition about the ongoing talks when we see repeated violations of the cessation of hostilities by the regime and supporting forces.”