(Updates with Obama meets Democratic and Republican leaders of the U.S. Senate and the House of Representatives) )
By Steve Holland
WASHINGTON, April 3 (Reuters) - President Barack Obama brought congressional leaders to the White House on Thursday for talks on the Ukraine crisis, with diplomatic efforts between the United States and Russia facing a hard slog.
A week after a trip to Europe that was dominated by meetings to discuss ways to react to Russia's annexation of Crimea, Obama sat down with Democratic and Republican leaders of the U.S. Senate and the House of Representatives.
Obama last spoke to Russian President Vladimir Putin on Friday by telephone. Since then, U.S. Secretary of State John Kerry has engaged in discussions with his Russian counterpart, Sergei Lavrov, about a diplomatic outcome to the dispute.
But no such resolution has presented itself, and Russia has shown no sign of loosening its grip on Crimea in what Moscow says is an effort to ensure the safety of ethnic Russians in the region.
Obama and European leaders agreed last week to impose sanctions against targeted sectors of the Russian economy, like its energy industry, should the Russian military move deeper into Ukraine.
The allies are also discussing ways to bolster NATO and increase the allied presence in member nations near Russia like the Baltic states of Latvia, Lithuania and Estonia.
A White House official said Obama and Vice President Joe Biden met with the two top Democrats in Washington, Senate Majority Leader Harry Reid and House Minority Leader Nancy Pelosi, and their Republican counterparts, House Speaker John Boehner and Senate Minority Leader Mitch McConnell.
Obama told them that "the United States continues to lead a coordinated international effort to support Ukraine and isolate Russia for its violation of Ukraine's sovereignty and territorial integrity," the White House official said.
Earlier on Thursday, Obama signed legislation passed earlier in the week by Congress to provide $1 billion in loan guarantees for the cash-strapped Ukraine government.
The White House official said Obama also discussed with the congressional leaders his participation in a nuclear security summit in Brussels and his talks with Pope Francis at the Vatican and with Saudi Arabia's King Abdullah near Riyadh.
But with Ukraine as the central foreign policy challenge in recent weeks, most of the more than hour-long meeting was about the standoff with Russia.
White House spokesman Jay Carney, at his daily news briefing, objected to Russia's increase in natural gas prices for Ukraine and said markets should determine prices.
He spoke after Russian natural gas producer Gazprom announced it would virtually double the gas price for Urkraine to $485 per 1,000 cubic meters this month, which Ukraine said was politically motivated.
"That kind of action taken coercively against Ukraine is something we oppose," Carney told reporters.
"We believe that markets should determine energy prices," he said. (Editing by Sandra Maler and Jan Paschal)