By Eric Yep 
 

Crude-oil futures held onto overnight gains in Asian trading hours Friday on heightened tensions between Ukraine and Russia that kept global financial markets on edge.

On the New York Mercantile Exchange, light, sweet crude futures for delivery in June traded at $101.92 a barrel at 0549 GMT, down $0.02 in the Globex electronic session. June Brent crude on London's ICE Futures exchange fell $0.01 to $110.32 a barrel.

Ukrainian forces killed several militants outside a pro-Russian stronghold in eastern Ukraine on Thursday as it attempted to regain control of the region, prompting Russian military exercises on its side of the border.

"With Russia warning of 'consequences' and Ukraine complaining of Russian 'interference' and 'permanent threats and blackmail,' worries over the possibility that escalation either via arms or sanctions could disrupt Russian oil and gas exports remained high," Citi Futures analyst Tim Evans said in a note.

U.S. President Barack Obama has also warned of further U.S. sanctions against Russia in coming days.

Standard & Poor's Ratings Services on Friday cut its rating on Russia to BBB-minus from BBB, saying the geopolitical situation in Ukraine could further weaken the country's growth prospects.

The ratings firm said Russia's fiscal dependency on commodity receipts has intensified in the last few years but commodity revenue will decline on the back of a slightly weaker oil price. S&P estimates that Russia needs an oil price of around $110 a barrel to balance this year's budget but expects the Brent oil price to fall to about $95 by 2015.

Nymex reformulated gasoline blendstock for May--the benchmark gasoline contract--fell 50 points to $3.0845 a gallon, while May heating oil traded at $3.0171, 26 points higher.

ICE gasoil for May changed hands at $929.00 a metric ton, up $2.50 from Thursday's settlement.

Write to Eric Yep at eric.yep@wsj.com