Emrah Gurel, Associated Press
U.S. Vice President Joe Biden arrives to address the annual Atlantic Council Energy and Economic Summit in Istanbul, Turkey, Saturday, Nov. 22, 2014.

ISTANBUL — U.S. Vice President Joe Biden on Saturday called on Europe to continue diversifying its energy supplies to reduce dependence on Russia, which he said should not be allowed to use its vast gas and oil resources as a geopolitical tool.

"Now, now, now is the time to act," Biden said, speaking at the Atlantic Council's energy security summit in Istanbul. "What's happening in Ukraine only underscores the urgency."

Russia, Ukraine and the European Union last month thrashed out a $4.6 billion deal that will guarantee Russian gas supplies to Ukraine and further on to the European Union. The deal eased fears that Europe will end up shivering this winter like it did in 2009, when a spat over Ukraine's gas bill prompted Russia to cut off energy supplies to Europe for nearly two weeks.

Moscow had cut off gas supplies to Ukraine in June over unpaid debts, a move that followed the ouster of Ukraine's Russia-friendly leader and the Kremlin's annexation of Crimea in March. Talks dragged on for five months amid fighting in eastern Ukraine between pro-Russian insurgents and government troops. But the looming onset of winter — a fierce, freezing season in Ukraine — gave the talks increased urgency.

"We have been aware that this single source of energy has been a problem for a long time," Biden said. "But my message is not that Europe can or should do away with Russian imports."

He said he had no doubt that Russia would continue to be a main energy supplier in the region.

"This is about energy security. To achieve it, Europe needs to ensure it diversifies," Biden said. "Russia can and should be a player, but Russia has to play by the rules."

Turkish Prime Minister Ahmet Davutoglu also spoke, outlining major diversification projects in the works.

"Energy should not be used as a weapon. ... Energy is a tool for peace," Davutoglu said.

Later in the day, Biden was scheduled to meet with Turkish President Recep Tayyip Erdogan.