Russia and the U.S. have "no common vision" on the crisis in Ukraine, Russia's foreign minister said Friday, March 14, after talks with his U.S. counterpart.

However Sergei Lavrov added that his meeting with John Kerry in London had been "constructive".

Russia would "respect the will of the people of Crimea", Lavrov said, ahead of Sunday's referendum there. Crimeans are to vote on whether to leave Ukraine and become part of the Russian Federation.

U.S. President Barack Obama said on Friday that there would be "consequences" if Ukraine's "sovereignty continues to be violated".

Lavrov told reporters in London that Russia had no plans to invade south-eastern Ukraine.

Russia's military intervention in the Crimean peninsula - part of Russia until 1954 and host to its Black Sea fleet - followed the fall of Ukraine's pro-Moscow President Viktor Yanukovych on Feb 22.

Moscow has not recognized the interim government that took over in Kiev following Yanukovych's departure.

The U.S. and the European Union have said that Sunday's vote in Crimea violates international law and the Ukrainian constitution, and are planning to impose sanctions against Russian officials if the crisis does not ease.