NEW YORK (AFP) - Global oil prices pushed higher on Thursday as tensions mounted over Russia's incursion into Ukraine's Crimean peninsula.

New York's main contract, West Texas Intermediate (WTI) for April delivery, added 11 cents, finishing at US$101.56 (S$128.31) a barrel.

Brent North Sea crude for April gained 34 cents at US$108.10 a barrel in London deals.

WTI prices were lower in early trade but spiked almost US$2, and Brent gained US$1, after US President Barack Obama toughly challenged Moscow's support for a referendum in Crimea on joining Russia.

"The proposed referendum on the future of Crimea would violate the Ukrainian constitution and violate international law," Mr Obama said.

"Any discussion about the future of Ukraine must include the legitimate government of Ukraine." "In 2014, we are well beyond the days when borders can be redrawn over the heads of democratic leaders," the US president said.

Earlier, the parliament in Crimea, under the de facto control of pro-Russian forces since the ousting of Ukrainian president Viktor Yanukovych, asked Russian President Vladimir Putin to examine a request for their region to join the Russian Federation.

Russia faces sanction from the US and Europeans which potentially could wreak turmoil in markets - especially as Russia is a crucial global energy producer and exporter of natural gas to Western Europe.

More than 70 per cent of its gas and oil exports to Europe pass through Ukraine.