Russia and the US are due to hold crucial talks to try to ease tensions over the Ukraine crisis.
US Secretary of State John Kerry and Russian Foreign Minister Sergei Lavrov are expected to meet on the sidelines of a long-planned conference on Lebanon in Paris.
The US accuses Moscow of deploying troops in Ukraine’s Crimea region, describing it as an “act of aggression” – a claim denied by the Kremlin.
Despite the sharp differences, both sides have hinted they would prefer to start a dialogue.
Moscow remains in de facto control of Ukraine’s southern autonomous region.
The tense stand-off continued overnight in Crimea, with reports that Russian forces have seized part of a Ukrainian missile defense unit.
In Donetsk, east of Ukraine, the regional government building has been evacuated and the area cordoned off amid unconfirmed reports of a bomb scare.
Earlier this week tensions escalated over Russia’s warnings that it could move beyond Crimea into eastern Ukraine to protect Russians and Russian-speakers there.
The move has triggered wide condemnation across the globe.
Meanwhile, NATO and Russia will hold talks in Brussels.
NATO chief Anders Fogh Rasmussen earlier said Russia continued to “violate Ukraine’s sovereignty and territorial integrity”.
On Tuesday, US President Barack Obama held a telephone conversation with German Chancellor Angela Merkel to discuss his plan to de-escalate the crisis, White House officials said.
They said Barack Obama’s offer to Moscow envisaged the return of the Russian troops in Crimea back to the bases of Russia’s Black Sea Fleet in the peninsula.
The plan – which Barack Obama discussed with President Vladimir Putin on Saturday – also calls for sending a group of international monitors to Ukraine to ensure the rights of ethnic Russians are protected.
And it encourages a direct dialogue between the government in Kiev and Moscow.
The Kremlin has so far not publicly commented on the offer.
Both President Vladimir Putin and Sergei Lavrov have said they want to see a government of national unity in Ukraine, with more representation for the Russian-speaking population in the east of the country.
[youtube kNbsxICELG0 650]