Russia is gathering thousands of troops at the border with Ukraine, calling the move practice for combat missions.
Russian Defense Minister Sergei Shoigu said about 10,000 troops are involved, along with various rocket launchers, tanks, and other weapons.
The military exercise comes as the fate of the Ukranian Pennisula of Crimea is still unclear.
On Sunday, voters will decide whether to remain part of Ukraine or to split and join Russia.
Meanwhile, Western countries are warning Russia it will face a backlash if it doesn't back down in Ukraine.
On Wednesday, the Senate Foreign Relations Committee moved forward in giving President Barack Obama power to sanction Russia for the invasion of Crimea.
"Putin has miscalculated by playing a game of Russian roulette with the international community, but we refuse to blink and will never accept this violation of international law," Sen. Bob Menendez, D-N.J., who introduced the bill, said.
During a meeting with Prime Minister Arseniy Yatsenyuk at the White House, Obama said the United States stands with the people of Ukraine.
The proposed legislation allows the Obama administration to impose economic sanctions on Russian officials for their part in the invasion.
It also authorizes $1 billion in loan guarantees to Ukraine's new government.