Grassley is referring to President Obama's ambassador to the United Nations, Susan Rice, who told members of the Security Council that the U.S. was “disgusted” by Russia and China's veto of a U.S.-sponsored resolution calling on Assad to step down. The resolution is based on a peace plan put forth by the Arab League.

Rice said the U.N. was being “held hostage” by the two permanent members, whose actions she said “sell out the Syrian people and support a craven tyrant.”

Obama himself weighed in on Saturday after the Syrian army reportedly killed more than 200 people in the city of Homs, the epicenter of the uprising against Assad's 12-year rule.

“The Syrian regime's policy of maintaining power by terrorizing its people only indicates its inherent weakness and inevitable collapse,” Obama said in a statement. “Assad has no right to lead Syria, and has lost all legitimacy with his people and the international community.”