US Secretary of State John Kerry will visit Kiev on Tuesday to lend support to Ukraine's new leaders, adding that Russian forces now control the Crimean peninsula.
"In Kiev, on March 4, Secretary Kerry will meet with senior representatives of Ukraine's new government, leaders of the Rada (parliament) and members of civil society," State Department spokeswoman Jen Psaki said on Monday.
Kerry "will reaffirm the United States' strong support for Ukrainian sovereignty, independence, territorial integrity".
He will also stress "the right of the Ukrainian people to determine their own future, without outside interference or provocation", Psaki added in a statement.
On a conference call with reporters, senior US administration officials repeatedly warned that Moscow risked a deepening fallout for sending its troops into southern Crimea.
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Economic talks, including a visit by a Russian delegation to discuss energy, have already been cancelled, and a coming major military event is also expected to be put on hold.
"We are also looking with allies and partners at a broad menu of options to curtail our economic and trade investment," a senior administration official said, adding that the US would likely "curtail normal activity that we have ongoing with Russia at this time".
The official said Russian forces were "now in complete operational control of the Crimean peninsula".
"They are flying in reinforcements and they are settling in."
The top US diplomat for Europe, Victoria Nuland, will travel to Vienna on Monday for talks with the Organisation for Security and Co-operation in Europe.
She was hoping to look at ways to get international monitors into flashpoint areas and possibly "a broader mission to replace Russian forces if the Russians can be persuaded to pull back", the official said.
