Russia’s foreign minister, Sergey Lavrov, has accused the West of plotting to control Ukraine.
He said the pro-Russian insurgents in the south east would lay down their arms only if the Ukrainian government clears out the Maidan protest camp in the capital Kiev.
“The West wants – and this is how it all began – to seize control of Ukraine because of their own political ambitions, not in the interests of the Ukrainian people,” Mr Lavrov said.
Russia and Ukraine reached an agreement in Geneva last week calling on all parties in the country to lay down arms and vacate public buildings.
Pro-Russian militia have been occupying government buildings in more than 10 cities in the eastern Ukraine while the nationalist Right Sector movement is still in control of two public buildings in Kiev.
The West has accused Russia of fuelling the unrest in Ukraine’s east and failing to use its influence on the pro-Russian insurgents.
“For seven days, Russia has refused to take a single concrete step in the right direction,” US Secretary of State John Kerry said.
“Not a single Russian official, not one, has publicly gone on television in Ukraine and called on the separatists to support the Geneva agreement, to support the stand-down, to give up their weapons, and get out of the Ukrainian buildings,” Mr Kerry said.
Mr Lavrov said the militia in the east “will be ready” to lay down arms and vacate the buildings “only if Kiev authorities get down to implementing the Geneva accords, clear out that shameful Maidan and liberate the buildings that have been illegally seized”.
Moscow in March recognised a hastily called referendum in Ukraine’s Black Sea peninsula of Crimea and annexed it weeks later, attracting condemnation of the West as well as sanctions targeting individuals.
Mr Kerry said that unless Moscow took immediate steps to de-escalate the situation, Washington would impose additional sanctions.
In south-eastern Ukraine, seven people were injured by a blast at a checkpoint set up by local authorities and pro-Ukraine activists outside the Black Sea port of Odessa. Local police spokesman Volodymyr Shablienko said unknown men had thrown a grenade at the checkpoint.
President Obama said the US and European leaders were laying the groundwork for sanctions against sectors of Russia’s economy if Moscow launches a military incursion into Ukraine.
He said he would call key European leaders last night to discuss what has happened since a deal was reached last week to de-escalate the crisis.
Russia’s involvement in Ukraine is already hurting Russia’s economy.
The Standard & Poor’s credit agency has cut Russia’s credit rating for the first time in more than five years. The ratings agency’s main concerns are the flight of capital and the risk to investment in Russia since the Ukraine crisis blew up late last year.
Credit ratings determine the cost of borrowing on international markets. Russian economic development minister Alexei Ulyukayev sought to play down the downgrade, calling it “partly politically motivated”.