The US reaction came after a crowd, inflamed by the downing of a Ukrainian military transport plane, tore down the embassy's flag and overturned vehicles as a dozen police looked on.
"The United States condemns the attack on the Russian Embassy in Kiev, and calls on Ukrainian authorities to meet their Vienna convention obligations to provide adequate security," State Department spokeswoman Jen Psaki said.
US Secretary of State John Kerry, meanwhile, called Ukraine Prime Minister Arseniy Yatsenyuk and expressed condolences for the 49 troops killed Saturday when pro-Russian rebels shot down the Il-76 transport plane near the airport that serves the city of Lugansk, a senior State Department official said.
The official, who spoke on condition of anonymity, said Kerry underscored to Yatsenyuk "the commitment of the United States and G7 partners to raise the costs for Russia if it does not end the flow of weapons across the border and break with separatists."
Kerry also called Russian Foreign Minister Sergei Lavrov, voicing the United States' "strong concern" about the transport of heavy weapons and militants across the Russian border into eastern Ukraine, and the downing of the transport plane.
"He pressed Foreign Minister Lavrov to make clear Russia's commitment to de-escalation and peace by ending the flow of weapons and support to separatists, and actively working with Ukraine for a ceasefire, amnesty, and political dialogue," the official said