(CNN) -- Russia sent mixed signals Wednesday on chemical weapons in Syria -- with its foreign ministry pinning the blame for one such attack on a rebel group hours after its president refused to close the door on a U.N.-approved strike against Syria's government. As one of Syria's top allies -- and one with veto power on the U.N. Security Council -- Moscow time and again has stymied efforts to punish Syrian President Bashar al-Assad's government for launching attacks killing innocent civilians and using weaponry derided by the international community. Such calls intensified after an alleged chemical weapons attack last month outside Damascus that, the U.S. government estimates, left upward of 1,400 people dead.
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NEW: An opposition group reports 72 deaths; state news says "terrorists" targeted
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NEW: Syrian official says "those who lead the aggression" will pay the price
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Russia's government links a rebel group to March chemical attack in Syria
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Russian leader says the evidence for a U.N.-backed strike should be undeniable
"We have absolute confidence that what our military undertakes to do, if it is ordered to do so, will degrade the capacity of @placeholder to use his weapons and serve as a very strong deterrent," Kerry said.