Russia has warned any US sanctions imposed on Moscow over the crisis in Ukraine will boomerang back on the United States, adding that Crimea has the right to self-determination as armed men tried to seize another Ukrainian military base on the peninsula.
In a telephone conversation with US Secretary of State John Kerry, Foreign Minister Sergey Lavrov warned against "hasty and reckless steps" that could harm Russian-American relations, the Foreign Ministry said on Friday.
"Sanctions ... would inevitably hit the United States like a boomerang," it added.
Kerry stressed the importance of resolving the situation through diplomacy and said he and Lavrov would continue to consult, the US State Department said.
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Russian President Vladimir Putin said after an hour-long call with US President Barack Obama that their positions on the former Soviet republic were still far apart.
The exchange comes as Russia declared its support for the breakaway movement in Crimea, welcoming a delegation from the autonomous republic in Moscow.
Obama announced the first sanctions against Russia on Thursday.
Putin, who later on Friday opened the Paralympic Games in Sochi which have been boycotted by a string of Western dignitaries, said Ukraine's new, pro-Western authorities had acted illegitimately over the eastern, southeastern and Crimea regions.
"Russia cannot ignore calls for help and it acts accordingly, in full compliance with international law," he said.
Serhiy Astakhov, an aide to the Ukrainian border guards' commander, said 30,000 Russian soldiers were now in Crimea, compared with the 11,000 permanently based with the Russian Black Sea fleet in the port of Sevastopol before the crisis.
The Pentagon estimated as many as 20,000 Russian troops may be in Crimea.
Putin denies the forces with no national insignia that are surrounding Ukrainian troops in their bases are under Moscow's command, although their vehicles have Russian military plates. The West has ridiculed his assertion.
On Saturday, Britain's Deputy Prime Minister Nick Clegg urged Putin to engage in a "civilised discussion" with the new government in Kiev.
"Putin's reaction is very revealing. It's as if he's been in a sort of deep freeze since the Cold War and hasn't moved with the times," Clegg said.
Former KGB spy Putin headed its successor, the Federal Security Service, shortly before he first became president in 2000.
"He gives every appearance of applying a KGB mentality rooted in the Cold War to new realities in 21st-century Europe," Clegg said.