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The Russian Foreign Ministry said the European Union has "made its choice against" a peace process in Ukraine by approving tougher sanctions against Russia.
President Barack Obama said the United States will join the European Union in imposing tougher sanctions on Russia's financial, energy and defence sectors after Moscow sent troops into eastern Ukraine last month.
"These measures will increase Russia's political isolation as well as the economic costs to Russia, especially in areas of importance to President Putin and those close to him," Obama said in a statement.
The President said the US will provide details on the new steps tomorrow.
The Russian rouble reached a new historic low against the dollar shortly after David Cameron said the European Union would introduce new sanctions against Russia on Friday.
At 1108 GMT the rouble was trading at 31.54, below its previous historic low of 37.51.
David Cameron has spoken to European leaders and agreed to push ahead with Russian sanctions by the end of the week, his spokesman has confirmed.
Russian president Vladimir Putin has ordered "snap checks" of his country's combat readiness in the far east, Itar Tass news agency reports.
Ambassadors of European Union countries have not yet reached a decision on whether to implement new sanctions against Russia, Brussels diplomats have said.
The EU figures said that while Germany was pushing to have the sanctions implemented, several other EU countries wanted to hold off because the ceasefire in Ukraine was holding.
Countries with close ties to Russia, including Italy, Austria and Finland were said to be reluctant to implement the new sanctions.
They added, however, that the general idea was still for the sanctions to be implemented through publication in the Official Journal of the European Union on Friday.
Pro-Kiev authorities in Mariupol, a frontline city in the conflict between Ukraine and pro-Russian separatists, have announced a night curfew and other restrictions for nearby towns and villages to help control rebel movements during a fragile ceasefire.
Some locals complained that the measures - which do not apply to the city of Mariupol itself - amounted to "undeclared martial law".
Others, however, said they were a necessary step enabling Ukrainian authorities to better monitor the shaky five-day ceasefire and prevent rebels exploiting it.
One military officer told Reuters: "This is not martial law. We want them to show themselves. If someone is out there between 8pm and 6am we will know they are not civilians and we can take appropriate measures."
Russia has carried out a successful test of its new Bulava intercontinental nuclear missile and will perform two more test launches in October and November, the head of its naval forces said.
The 12-metre long Bulava, or mace, has undergone numerous tests, some of which have failed, causing setbacks for the project that aims to be the cornerstone of Russia's nuclear arsenal over the next decade.
Drones will be deployed to monitor the ceasefire in Ukraine. The chairman of the Organisation for Security and Cooperation in Europe (OSCE), Didier Burkhalter, said their drones will be sent into the field soon.
He added the organisation is also holding talks on the possibility of using national drones as soon as possible as "in-kind contribution by participating states" in the monitoring scheme.
Ukraine's President Petro Poroshenko says it is "difficult" to maintain the ceasefire because "terrorists are trying all the time to provoke" Kiev's troops.
He told a televised meeting of the government that Ukraine is "regrouping" its forces in the east of the country to defend territory, not to stage a new offensive.
He said the peace roadmap agreed last week between Ukraine and pro-Russian separatists preserves the concept of a sovereign, united Ukraine within its current borders.
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