The strikes came less than a week into a fragile ceasefire aimed at stopping the bloodshed in Syria's five-year civil war, as Russia accused what it termed "moderate rebels" of causing the truce to fail.
American officials said on yesterday the US-led coalition fighting the Islamic State (IS) group in Syria may have hit Syrian military positions.
"Coalition forces believed they were striking a Daesh fighting position," a Pentagon statement said, using an Arabic acronym for the IS group.
Russia has requested an urgent UN Security Council meeting, which diplomats said was set to start at 2330 GMT yesterday.
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"We demand Washington's full and detailed explanation, and that must be made before the UN Security Council," said Russian foreign ministry spokeswoman Maria Zakharova.
The Syrian Observatory for Human Rights monitoring group gave a toll of 83 soldiers killed, as it confirmed the strikes were US-led coalition raids.
The situation in Syria is deteriorating, the Russian military said earlier, adding that the United States would be responsible if a fragile ceasefire in force since Monday collapses.
"Sixty-two Syrian soldiers were killed and a hundred others were injured in these strikes."
The Russian military said two F-16 and two A-10 jets that flew into Syrian airspace from neighbouring Iraq carried out the 1400 GMT attack.
"Straight after the coalition's strikes, IS militants launched an offensive," said the statement, adding that "fierce fighting against the terrorists" ensued nearby.
"If these strikes were due to an error in the target coordinates, that would be a direct consequence of the US' refusal to coordinate with Russia its fight against the terrorist groups in Syria," it said.
The Observatory also reported that "20 members of IS were killed and dozens more wounded in heavy Russian strikes on Jabal Therdeh".
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