Ukrainian Prime Minister Arseniy Yatsenyuk is preparing a diplomatic push on his nation's political crisis.
Mr. Yatsenyuk is due in Washington for talks Wednesday with U.S. President Barack Obama. The two leaders are to discuss the standoff over Crimea, the strategic southern Ukrainian peninsula with a Russian-speaking majority.
Meanwhile, the Crimean government on Monday officially invited the Organization for Security and Cooperation in Europe to monitor a March 16 referendum hat will ask voters if they would like Crimea to become part of Russia..
OSCE monitoring groups have been turned away from the Crimean border by armed men at least three times in the past week.
U.S. federal agents have arrived in Ukraine to help the nation's interim leaders investigate allegations of corruption by Mr. Yanukovych during his tenure. The U.S. Ambassador to Ukraine said Monday the investigators are also looking into whether some assets can be recovered.
Russian Foreign Minister Sergei Lavrov said in a televised meeting with President Vladimir Putin that Russia and the West continue to differ over Ukraine.
Lavrov complained Western proposals forwarded by U.S. Secretary of State John Kerry amounted to "moving forward on the basis of a situation born out of a state coup." Moscow has consistently described the ouster of former Ukrainian president Viktor Yanukovych as the illegal overthrow of a legitimate head of state.
Lavrov also said Kerry had accepted an invitation to visit Russia for further talks on the crisis, but then changed his mind and postponed the visit. Lavrov said Russia will offer its own proposals to resolve the Ukraine crisis.
Russian news agencies report Mr. Yanukovych is expected on Tuesday to make his second public appearance since stepping down and fleeing Kyiv last month. There were no details about the content of his address.
Earlier Monday, the chief of Crimea's election commission, Myhkailo Malyshev, said he is moving ahead with preparations for next Sunday's referendum on unification with Russia. He said all registered Crimean voters are eligible to vote.
"All citizens who are registered in the territory of the Autonomous Republic of Crimea have the right to vote at this referendum, meaning that nothing will prevent them from voting."
Russian forces have tightened their grip on Crimea, as authorities in the breakaway territory push their plan to join Moscow.
Interim prime ministerYatsenyuk has vowed not to give up "a single centimeter" of territory.
A Russian lawmaker said the Kremlin had set aside $1.1 billion to rebuild Crimea's industrial infrastructure if the disputed region votes in a March 16 referendum to join Russia.
U.S. Deputy National Security Adviser Tony Blinken says Washington will not recognize the annexation of Crimea by Russia if residents of the region vote to leave Ukraine.
Former U.S. ambassador to Russia Michael McFaul told VOA the annexation will "isolate Russia from the rest of the world for years to come, maybe even decades to come." He said "Even the Chinese are not supporting Russia in this act - nobody thinks this act is legitimate."
Russian forces tightened their grip on the peninsula taking over a Ukrainian border post on the western edge of Crimea, trapping about 30 personnel inside. A Ukrainian military spokesman said Russian forces now control 11 border guard posts across the territory.
Russia denies it has troops on the peninsula beyond those regularly stationed with its Sevastopol-based Black Sea fleet. Ukraine's much smaller navy is also based in the Crimean port city. Witnesses say although the soldiers have no insignia identifying them, they are clearly Russian.
Foreign observers have failed to get into Crimea to get a first-hand look at the situation and were forced to turn back Saturday after pro-Kremlin gunmen fired warning shots.