New York's West Texas Intermediate for June delivery, climbed five cents to $100.89 in mid-morning trade while Brent North Sea crude rose 15 cents to $108.27 for its June contract.

The United States and Europe on Monday hit Russia with fresh sanctions for failing to stop soaring tensions in Ukraine, where a pro-Moscow mayor was shot and badly wounded as rebels seized another town.

The White House imposed sanctions on seven Russian officials and 17 firms close to President Vladimir Putin, as Western powers stepped up the pressure on Moscow over the worst East-West crisis since the Cold War.

But Desmond Chua, an analyst at CMC markets in Singapore said that they were "less aggressive than most would have thought".

Ukraine, a major conduit for Russian natural gas exports to Western Europe, is monitored closely by investors who are concerned that a full-scale armed conflict will disrupt supplies and send energy prices soaring.