Secretary of State John Kerry accused Russia on Sunday of "grandstanding" and "showboating" after its Defense Ministry said U.S. airstrikes killed 62 Syrian soldiers and wounded 100 others.
The comments came during an interview with CNN nearly one week after an increasingly fragile, U.S.-Russia-negotiated ceasefire between government and opposition forces in Syria took effect.
Kerry said Syrian President Bashar al-Assad. an ally of Russia's, has continued "indiscriminate" bombing and is "the single biggest blockade" for Syrians desperate for humanitarian aid.
"The biggest judgment they need to make is to stop Assad from bombing people indiscriminately, which he continues to do," Kerry said. "If you are serious about having a cease-fire, and they say they are, then they should keep Assad from flying right now."
Kerry added: "So we call on Russia to stop the grandstanding, stop the showboating and get the humanitarian assistance going."
Related: Syria Cease-Fire Appears to Be Holding, Aid Convoys on Standby
Russia called an emergency meeting of the U.N. Security Council over the incident Saturday night, and its Defense Ministry accused the United STates of violating the cease-fire.
In a statement, the ministry said the apparent strikes were "a direct consequence of the American side's stubborn reluctance to coordinate with Russia their anti-terrorist operations in Syria."
A senior U.S. defense official disputed that, telling NBC News that the U.S. military went "above and beyond" current information-sharing requirements between the two countries.
U.S. Central Command said earlier that coalition forces believed they were striking an ISIS target.