Oil extended gains above $70 a barrel in Asian trade on Friday as attacks on pipelines in crude producer Nigeria escalated and the US dollar wobbled from a recent rally, analysts said.

In morning trade, New York's main futures contract, light sweet crude for delivery in August, climbed 24 cents to $70.47 a barrel.

Brent North Sea crude for August was up 35 cents to 70.13.

Nigerian rebels on Thursday said they carried out a pre- dawn attack against Royal Dutch Shell facilities in a warning to Russia not to invest in the country's oil and gas industry.

"The news from Nigeria (about) more attacks on oil facilities and the fact that two refineries are now shut down are supporting the market," said Andy Lipow, president at Lipow Oil Associates.

Other analysts said oil prices also had support from a weaker US dollar, which rallied briefly after a US central bank announcement Wednesday that it will maintain its monetary policy and keep interest rates at near zero.

The Fed's action helped lift the stock market and encouraged riskier market bets, which staunched the dollar rally.