In a telephone conversation with US Secretary of State John Kerry, Russian Foreign Minister Sergei 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 State Department said.

It was the second tense, high-level exchange between the former Cold War foes in 24 hours over the pro-Russian takeover of Ukraine's Crimean peninsula.

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. Obama announced the first sanctions against Russia on Thursday.

Putin, who later 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.

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.

Ukraine has been gripped by unrest since November 2013, when ousted president, Viktor Yanukovych, refrained from signing an Association Agreement with the European Union in favor of closer ties with Russia.

On February 23, amid rising violence in Ukraine, the parliament ousted Yanukovych and named Oleksandr Turchynov, the legislature’s speaker, as interim president.

NTJ/MB