Sept. 11, 2016 9:16 a.m. ET
BEIRUT—The death toll from airstrikes in the rebel-held areas of Syria’s Idlib and Aleppo provinces rose to at least 90 people, a monitoring group said Sunday, ahead of a cease-fire agreed on by the U.S. and Russia coming into effect across the war-torn country.
Warplanes struck a market in Idlib city on Saturday, killing at least 58 people—of which 13 were children and another 13 were women—and wounding several others, according to the U.K.-based Syrian Observatory for Human Rights. The death toll is expected to rise as some people were in critical condition, it said. Another two people were killed in a nearby town.
At least 30 people were also killed and many others wounded in airstrikes in and around Aleppo, the scene of an escalating battle and humanitarian crisis, the monitoring group said.
The Syrian conflict has cost the lives of some 400,000 Syrians since 2011, according to the United Nations’ special envoy for Syria.
Though the truce is nationwide, the northwestern province of Idlib will remain a target. The province is almost entirely under the control of a coalition of rebel groups, one of which, Syria Conquest Front, was formerly known as the al Qaeda-affiliated Nusra Front.
The deal was welcomed by the main parties in the conflict and several world leaders as a chance to ease the humanitarian crisis in the country.
Iran, a key ally of Syrian President Bashar al-Assad alongside Russia, was positive about the deal, according to the official Islamic Republic News Agency, though Hossein Jaber Ansari, Iran’s deputy foreign minister for Arab and African affairs, said a lasting solution needed to combine humanitarian, political and security elements.
“Terrorist groups have disrupted the security of this country, the region and the world by their widespread presence,” he said. “Therefore, any solution or agreement without considering this aspect will be futile.”
Syria’s main opposition group on Saturday said it was “cautiously optimistic” about the cease-fire agreement, as it would allow humanitarian aid to reach besieged areas and save lives.
“We in the Syrian National Coalition are always with any initiative or agreement that aims to protect civilians and end the suffering of the people [especially] in besieged areas,” Anas Abdah, president of Syria’s main political opposition group, told The Wall Street Journal.
Mr. Abdah said it was unclear if the regime and its allies, particularly Russia, would stick to the agreement, but he welcomed any deal that would protect Syrian civilians.
Syria’s state news agency SANA reported on Saturday that the Syrian government had agreed to the cease-fire deal and that there would be a cessation of hostilities in Aleppo city for humanitarian purposes.
It wasn’t immediately clear what deterrents would be set up to prevent both sides from violating the cease-fire, or whether mechanisms were in place to hold any parties accountable.
“We need to see the agreement and study it carefully,” Mr. Abdah said. “The devil is in the details. So unless we see the details, it’s really difficult to come up with an accurate position.”
Turkey—which has emerged as a key player in the Syria conflict, working with the U.S. and improving its relationship with Russia—welcomed the deal, and urged a political settlement to the conflict that is ravaging its southern neighbor, just two weeks after its forces launched cross-border operations in Syria.
Federica Mogherini, the European Union’s foreign policy chief, asked all parties in the conflict to ensure its effective implementation. This, she said, would “enable the lifting of all sieges and allow sustained, countrywide humanitarian access to those in need as well as progress on the issue of detainees and missing persons.”
U.K. Foreign Secretary Boris Johnson said it was vital that the regime in Damascus now delivers on its obligations, and called on Russia to use all its influence to ensure this happens.
As part of the deal, once violence is reduced and aid groups receive humanitarian access to the battle-scarred Aleppo area, the U.S. and Russia would begin working out of a “joint implementation center” to continue the fight against the Syria Conquest Front and Islamic State militants.
Some activists in Syria said a cease-fire is likely to end the killing of innocent civilians, but they remained distrustful of the Assad government.
“Even if the regime abided by the agreement at the beginning, it will [violate] it later,” said Osama Abu Zaid, an activist based in Homs.
He added that the cease-fire is likely to fail because the Syria Conquest Front fights alongside moderate opposition fighters.
The Nusra Front was rebranded in July as Syria Conquest Front in an effort to distance it from al Qaeda and to get the U.S. to stop targeting the group. It is considered to be the strongest and most disciplined Syrian rebel group among dozens of fractured and disorganized factions currently fighting government forces.
—Emre Peker, Felicia Schwartz and Aresu Eqbali contributed to this article.
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