The U.S. ambassador to the United Nations tells Russia it is "long past time" to stop covering for Syrian President Bashar al-Assad.
"You are isolating yourselves from the international community every time one of Assad's planes drop another barrel bomb on civilians and every time Assad tries to starve another community to death," Nikki Haley told the UN Security Council on April 12.
"We can start by working together to deescalate" the six-year civil war in Syria, Haley also said.
Tension between Russia and the United States has risen since a suspected chemical attack on the rebel-held Syrian town of Khan Sheikhoun last week that left more than 80 people dead.
Haley warned that the United States will not allow any further use of chemical weapons "to go unanswered."
Earlier, Russian Deputy Foreign Minister Gennady Gatilov told the Interfax news agency that a Western-backed draft Security Council resolution on the April 4 incident was "unacceptable" in its current form.
The United States and other Western governments have rejected assertions by Damascus and Moscow, Assad's main backer in the Syrian conflict, that deadly gas was released when government air strikes hit rebel-controlled chemical weapons.