Power said it was "a plan that would free Russia from the commitment it made in Minsk to withdraw its fighters and return control over the international border to Ukraine.
"The plan would seek to legitimize territorial gains made by separatists in September as well as Russian personnel and equipment on the territory of Ukraine," U.S. Ambassador Samantha Power said.
She said that such peace plans are well known as in the case with Abkhazia, South Ossetia, and Transnistria. Putin floated the proposal to end a conflict in which more than 4,800 people have died since last April to Ukrainian President Petro Poroshenko last week. But Moscow said on Sunday Poroshenko rejected the plan. Putin's spokesman said the proposal called for a cease-fire by government forces and separatist militiamen in southeastern Ukraine, and the withdrawal of heavy artillery by both sides. "Time and again President Putin has extended an olive branch in one hand while passing out grad missiles and tanks with the other. Let us pull the veil away from Putin's peace plan and call it for what it is - a Russian occupation plan," she said.
Power was referring to a peace plan agreed in Minsk, Belarus, last September between Ukraine, Russia and pro-Russian separatist leaders to end the war.
Russian Ambassador Vitaly Churkin blamed Kiev for the recent upsurge in violence and said Moscow was ensuring "full compliance with the Minsk agreement."
The Minsk plan provides for a cease-fire and withdrawal of foreign fighters and military equipment from Ukraine. The cease-fire has been very shaky from the start, and hundreds have died since September in clashes Kyiv says have involved regular Russian troops.
British Ambassador Mark Lyall Grant joined the criticism of Moscow, citing "the usual pattern of Russian denials and misinformation." He also called on Moscow to stop using humanitarian convoys to supply rebels with arms.