Brent Climbs Above $108/bbl on U.S.-Russian Tensions, Supply Fears

The spread between the two benchmarks widened to close at $6.30.

Russian Foreign Ministry said the United States was trying to influence international opinion through unfounded insinuations over the crisis in Ukraine.

"If the U.S. makes the case that Russia is actually firing Ukrainian planes, that is a game-changer," said Phil Flynn, an analyst at Price Futures Group in Chicago. "It will put further pressure on the European Union to impose significant sanctions on Russia."

Continued violence in Libya and Israel provided further support for oil prices.

In Libya, oil production has risen to 500,000 barrels per day, but there was no progress on reopening its Brega oil port after an agreement to end a protest there.

Authorities in Gaza said Israeli forces shelled a shelter at a U.N.-run school on Thursday, killing at least 15 people as the Palestinian death toll in the conflict exceeded 760 and attempts at a truce remained elusive.

Oil prices were also supported by U.S. Labor Department unemployment data, which suggested the economic recovery remained on track with initial weekly jobless claims at their lowest since February 2006.