Syria's fragile peace talks appeared doomed Tuesday after airstrikes killed around 40 people in a crowded vegetable market in rebel territory, with the opposition saying a truce was finished and it would keep away from negotiations indefinitely.

France described the bloodshed as "another massacre." A monitoring group said it believed the strike on the market in Maarat al-Numan in Idlib province was the deadliest single attack since a partial ceasefire took effect Feb. 27.

A rescue worker said warplanes had simultaneously struck crowded markets in two towns in Idlib, killing at least 38 people in Maarat al-Numan and 10 others in nearby Kafr Nubl.

"We have more than 20 cars that have been moving dead and injured to hospitals in the area," said Ahmad Sheikho, a member of the  Civil Defense Corps, a rescue service operating in opposition-held territory.

The airstrikes, accompanied by intense fighting in other areas, appears to leave the fragile 6-week-old ceasefire in tatters. The truce was brokered by the United States and Russia to pave way for the first peace talks attended by the warring factions since fighting began five years ago.

Those talks, taking place under U.N. auspices in Geneva, also appear to have collapsed this week. The opposition says it has called a "pause" to negotiations, although it is reluctant to accept blame for the collapse by walking out altogether.

It was not immediately clear whose aircraft were responsible for the strikes. Both Syria's own air force and that of its Russian allies have been operating despite the truce.

Damascus and Moscow say they are attacking only territory held by Islamic extremist fighters who are not covered by the ceasefire, but opposition groups dismiss this, saying the government and its Russian allies use those militants to justify wider attacks.

The Britain-based Syrian Observatory for Human Rights, which monitors the conflict through a network of sources on the ground, said 37 people were killed in Maarat al-Numan and seven in Kafr Nubl. Many of the injured were in a serious condition, and the death toll was expected to rise, it said.

Asked if it was the deadliest attack recorded since the ceasefire began, the Observatory's head, Rami Abdulrahman, said: "I believe so."

'Another Massacre'

Ahmed al-Seoud, head of the 13th Division, a foreign-backed faction fighting under the umbrella of the Free Syrian Army, also gave a death toll of around 40 in the larger attack and said 80 people were wounded.

"We learned today there had been another massacre this morning," French envoy Franck Gellet said in Geneva.

The Syrian military could not immediately be reached for comment, and state news agency SANA made no mention of airstrikes in Idlib.

As fighting raged and air strikes on rebel-held areas intensified, the opposition urged foreign states to supply them with the means to defend themselves, a thinly veiled reference to the anti-aircraft weapons long sought by insurgents.

U.S. President Barack Obama told Russia's Vladimir Putin in a phone call Monday that Syria was starting to fray more rapidly. The two Cold War-era superpowers are joint sponsors of the peace process and ceasefire, after intensifying diplomacy following Russia's decision last year to join the war, an intervention that tipped momentum Assad's way.

The Geneva talks aim to end a war that has killed more than 250,000 people, created the world's worst refugee crisis since WWII, allowed for the rise of the Islamic State group and drawn in regional and major powers.

Damascus blames the rebels for breaking the cessation of hostilities. Chief Syrian government negotiator Bashar Ja'afari said his team was pushing for an expanded government as a solution to the war, an idea rejected by the armed opposition, which has fought for five years to oust Assad.

With fighting reported across much of northwest Syria on Tuesday, both sides were obdurate.

"Our mandate in Geneva stops at forming a national unity government," Ja'afari told Reuters. "We have no mandate whatsoever either to address the constitutional issue, meaning establishing a new constitution, or addressing parliamentary elections or addressing the fate of the presidency.

"It's not the business of anybody in Geneva. It happens when the Syrian people decide," he said in an interview.

Assad is 'Dreaming'

Riad Hijab, chief coordinator of the main opposition HNC bloc, said he would leave Geneva, although experts would stay to discuss certain issues. There was no chance of returning to the main talks while the government broke the truce, blocked humanitarian access and ignored the issue of detainees.

Clearly angry, Hijab dismissed any suggestion that Assad could stay in power, saying he was "dreaming." Major powers were paralyzed and needed to re-evaluate the truce and the humanitarian situation, Hijab said.

Another opposition figure made clear the suspension of talks was indefinite.

"There is no date. The date ... is the implementation of matters on the ground, and likewise the correction of the path of negotiations. All the while that does not happen, the time period will remain open," the opposition's George Sabra said.

The opposition also had "big complaints" about U.S. policy, which he said sought to carry on talks "without us obtaining anything real," he said. He called on international powers to supply Syrians with the means to defend themselves.

Syrian forces backed by Russian warplanes launched a counterattack against rebels in the northwestern province of Latakia, a rebel group and the observatory reported.

Targets included towns and villages where the truce agreement had brought about a lull in fighting. Fighters predicted more bloodshed.

"Let's be realistic. The escalation will start," said Bashar al-Zoubi, a prominent rebel leader.

Ahmed Al-Seoud, the head of another rebel group, said he hoped for more military support from Assad's foreign enemies.

Rockets fired by insurgents killed three children in Kefraya, a Shi'ite town loyal to the government, the observatory said. State media said the dead were members of one family.

Fighting in Latakia focused on areas where insurgent groups had launched an attack on government forces Monday and where battles had often erupted despite the cessation of hostilities.

"The regime is trying to storm the area, with the participation of Russian helicopters and Sukhoi [warplanes]," said Fadi Ahmad, spokesman for the First Coastal rebel group in the area. The observatory said fighting had raged since morning.

Government airstrikes were also reported in northern areas of Homs province under rebel control.