Russian President Vladimir Putin said Tuesday there was no need to send Russian troops to Ukraine at this time.
"The possibility exists," however, that such a move might be made, Putin said during a gathering with reporters broadcast by state television.
"What would be the reason for using the armed forces? Obviously, in an extreme case," Putin said.
Russia "has a request (to deploy troops) from the legitimate president of Ukraine," Putin said, referring to Viktor Yanukovych.
Yanukovych, who was ousted last month, is in Russia.
"In fact, if we make the decision, if I make the decision to use the armed forces, it will be legitimate," the Russian leader said.
Russian and Ukrainian soldiers "will not be on different sides of the barricades, they will be on the same side," Putin said.
Many Russian and Ukrainian military commanders "know each other personally," Putin said.
Russia does not plan to annex Crimea, an autonomous Ukrainian republic, Putin said.
Moscow deployed its forces last week in the Crimean Peninsula, a majority Russian-speaking region, claiming it was protecting ethnic Russians and Russia's interests in the area.
Russia's Black Sea Fleet is based in the Crimean port city of Sevastopol, which has been the home of the naval force since the 18th century.
The Crimean Peninsula, located on the northern coast of the Black Sea, is home to 2 million people; ethnic Russians make up 60 percent of the population, while 25 percent of residents are ethnic Ukrainians and 12 percent are Crimean Tatars.
Putin said the takeover of Ukraine's government was "an unconstitutional coup" and an armed insurrection.
The Russian leader warned the West that imposing economic sanctions on Moscow would be counterproductive and hurt all the parties involved.
"The ones who are thinking about the consequences (of the sanctions) should first think about the ones who want to impose them. In the contemporary world, where everything is linked and everyone depends on everyone else in some way, you can, of course, do damage to others, but it will be mutual damage," Putin told reporters.
The Russian leader took a shot at the United States and its support for the opposition protests that led to Yanukovych's ouster.
The crisis that led to Yanukovych's ouster erupted at the end of November, when Yanukovych backed away from plans to ink a pact with the European Union and instead signed a $15 billion financial-aid package with Russia.
Protesters took to the streets of Kiev and began occupying administrative buildings, prompting Ukraine's parliament, then controlled by Yanukovych's allies, to pass a package of laws on Jan. 16 restricting freedom of assembly, freedom of speech and other basic rights.
Violent clashes pitting demonstrators and riot police broke out three days later and left six dead and hundreds wounded.
Ukrainian officials and opposition leaders began seeking a negotiated solution to the crisis in the wake of the bloodshed.
The talks led to the resignation of Prime Minister Mykola Azarov on Jan. 28 and the repeal of the controversial anti-protest laws.
But more street battles pitting pro-European Union protesters against the security forces left dozens dead in February, and led to Yanukovych agreeing to call early presidential elections and then fleeing Kiev.
After Yanukovych left the city, many of his former allies in parliament turned against him and helped oust him from power and release his arch-rival, the Fatherland's Yulia Tymoshenko, from prison.
She has reportedly announced her candidacy in the presidential election, which has been moved up to May 25.
"I sometimes get the impression that over there in America, on the other side of the big pond, some laboratories experiment (with countries) like they are rats, without understanding the consequences of what they do," Putin said.
U.S. Secretary of State John Kerry arrived Tuesday in Kiev, where he plans to meet with officials from Ukraine's interim government. EFE