Russia's president has flipped the switch to open the last of four electricity lines to Crimea aimed at allowing the Russia-annexed peninsula to end its reliance on Ukrainian power.

The line from the Russian mainland that Vladimir Putin inaugurated on Wednesday brings Russia's electricity supply to Crimea to 800 megawatts a day.

Russia annexed Crimea in March 2014, after it sent in troops in the wake of the ouster of Ukraine's Russia-friendly president and a dubious referendum on the peninsula about joining Russia. After annexation, Crimea continued to buy electricity from Ukraine, but last year experienced severe shortages after protesters blew up power lines leading to Crimea.

Russia's so-called Crimean "energy bridge," including four undersea cables, cost 47 billion rubles ($725 million), the state news agency Tass reported.