Russia has said it had nothing to do with air strikes on a school in Syria's rebel-held Idlib province that killed 22 children.
"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.
Ms Zakharova said claims that Russian and Syrian warplanes had conducted the deadly air strikes in Idlib on Wednesday were "a lie".
The raids hit a school and the surrounding area, killing 22 children and six teachers, the United Nations children's agency UNICEF said.
The Syrian Observatory for Human Rights monitor said "warplanes - either Russian or Syrian - carried out six strikes" in the village of Hass, including on a school complex.
UN Secretary-General Ban Ki-moon called for an immediate investigation, saying: "If deliberate, this attack may amount to a war crime."
He also raised concerns about a series of attacks on civilian targets in Syria, now in its sixth year of war.
"If such horrific acts persist despite global outrage, it is largely because their authors, whether in corridors of power or in insurgent redoubts, do not fear justice," he said.
"They must be proved wrong."
Russia's defence ministry also denied any involvement in the incident.
"On Wednesday, October 26, not one Russian warplane entered that area," ministry spokesman Igor Konashenkov said in a statement.
"This is an absolute fact."
Mr Konashenkov added that photographs taken by a Russian drone showed that the roof of the school reportedly hit in the strikes showed no damage and that there were no craters attributable to bombs in the area.
The West has accused Moscow of bombing the war-torn country's civilian infrastructure to bolster long-time ally President Bashar al-Assad.
Western powers and rights groups have also accused Russia of perpetrating potential war crimes in air strikes in rebel-held eastern Aleppo in support of a brutal Syrian government offensive to retake total control over the city.
Russia's defence ministry said yesterday that Syrian and Russian warplanes had not bombed Aleppo in the past nine days.
A ceasefire meant to allow civilians and armed combatants to leave eastern Aleppo ended at the weekend, with Russia on Monday ruling out an extension of the truce for the time being.
