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WHITE HOUSE — President Barack Obama welcomed interim Ukrainian Prime Minister Arseniy Yatsenyuk to the White House Wednesday as part of U.S. efforts to defuse the growing crisis between Washington and Moscow over the situation in Ukraine's Crimean region.

Prime Minister Yatsenyuk was welcomed at the White House with all the fanfare of a head of state visit as Obama hosted the Ukrainian leader in the Oval Office. The welcome was meant as a sign that Ukraine's new government has U.S. support and recognition.

"It is a pleasure to welcome Prime Minister Yatsenyuk to the Oval Office, to the White House. I think all of us have seen the courage of the Ukrainian people in standing up on behalf of democracy,” said Obama/

The message is meant for Russia and is Washington's latest attempt to get the Russians to call their troops back to their bases from the positions they have taken in Ukraine's Crimea region.

Despite U.S. efforts to reduce tensions, the crisis is deepening, as a Russian-sponsored referendum draws near in Crimea that could decide whether the region splits off from Ukraine and potentially joins Russia.

Obama said Russia could choose another path.

"We will not recognize, certainly, any referendum that goes forward. My hope is that as a consequence of diplomatic efforts over the next several days, that there will be a rethinking of the process that's been put forward," said Obama.

The Ukrainian leader thanked Obama for his support.

"Mr. President, it is all about the freedom. We fight for our freedom. We fight for our independence. We fight for our sovereignty and we will never surrender," said Yatsenyuk.

The United States has sent additional warplanes to central Europe, but maintains it does not want a military solution.

Washington announced it is now enforcing visa restrictions laid out last week - part of the cost that Washington said Moscow will pay if it does not stop interfering in Crimea.

Secretary of State John Kerry met with the Ukrainian leader and will later head to London for more difficult talks with his Russian counterpart, Sergei Lavrov.

Whether the strong words have any effect on Russia's actions remains to be seen.

"We can say all we want, but Putin has taken Crimea and that's a fact. And I think we have to draw a distinction. If we want our words of unacceptability, of not recognizing this as not being legitimate. If we want those words to mean something, we also have to be prepared to take actions," said Kurt Volker, a former U.S. ambassador to NATO.

Ukraine's new leader leaves Washington with a package of U.S. support to boost his fragile government, including $1 billion in loan guarantees that are pending congressional approval.