The U.N. Children's agency called the airstrikes in Syria's opposition-held northern Idlib province a day earlier an "outrage," suggesting it may be the deadliest attack on a school since the country's war began nearly six years ago. The attack, according to UNICEF, killed 22 children and six of their teachers.Russia said Thursday it had nothing to do with air strikes on a school in Syria's opposition-held Idlib province. "The Russian Federation has nothing to do with this terrible tragedy, with this attack," foreign ministry spokeswoman Maria Zakharova said, adding that Moscow demanded an immediate investigation. Asked about the school attack, Russia's UN ambassador Vitaly Churkin responded, "It's horrible, horrible. I hope we were not involved."A series of airstrikes in the village of Hass around midday Wednesday hit a residential compound that houses a school complex as children gathered outside. The Syrian Civil Defense first responders team and the Britain-based Syrian Observatory for Human Rights said yesterday the airstrikes killed at least 35, most of them children. Initially, the estimated death toll was 22. The civil defense said there were two schools in the area where the airstrikes hit around midday.UNICEF Executive Director Anthony Lake called the airstrikes an outrage. He added if found to be deliberate, the attacks would be considered a war crime."This latest atrocity may be the deadliest attack on a school since the war began more than five years ago," Lake said in a statement. "When will the world's revulsion at such barbarity be matched by insistence that this must stop?"Idlib, the main Syrian opposition stronghold, has regularly been hit by Russia-backed Assad's warplanes as well as the U.S.-led coalition targeting Daesh militants. An activist at the scene said as many as 10 airstrikes were believed to have hit the residential area Wednesday.UNICEF said since the beginning of 2016, it has verified at least 38 attacks on schools around Syria. Before Wednesday's attack, 32 children were killed in 2016 in attacks on schools, according to Juliette Touma, regional UNICEF chief of communication. A total of 60 attacks were recorded on schools in 2015. Touma said 591 children were killed in 2015 as a result of the ongoing conflict in Syria, including in attacks on schools. "In general there are one in three schools in Syria that can't be used anymore because they were damaged or destroyed or used for military purposes or sheltering the displaced," she told The Associated Press, speaking from Amman, Jordan.Russian and the Bashar-Al Assads' warplanes have not flown closer than 10 kilometers (6.21 miles) of Syria's Aleppo for nine days, the Russian defense ministry said on yesterday. In response to UN's accusation of Assad forces in Aleppo bombing, "If you have any information that there were any missile and bomb strikes, please provide this information," Russia's Permanent Representative to the United Nations Vitaly Churkin said Thursday, as Russian news agency TASS reported.