New York's main contract, West Texas Intermediate for May delivery, dipped 22 cents to $104.08 in mid-morning trade and Brent North Sea crude for June eased 44 cents to $109.09 a barrel.

Desmond Chua, market analyst at CMC Markets in Singapore, said trading volumes are thin in Asian trade after the long Easter weekend.

Financial markets in Hong Kong, Australia and New Zealand are closed for public holidays.

However, investors were increasingly concerned about the Ukraine crisis, Chua said.

A deadly gunfight in a town in the east of the country on Sunday killed at least two pro-Kremlin rebels, shattering an Easter truce and raising fears that Russia would send in troops to the ex-Soviet state.

The attack undermined an accord worked out in Geneva last week between Russia, Ukraine and Western powers for pro-Russian rebel groups to surrender their weapons.

There are concerns that any full-scale armed conflict in the region will disrupt supplies and send oil and gas prices rocketing because Ukraine is a major conduit for Russian gas to western Europe.

Chua said investors will next be focusing on United States first quarter corporate earnings data to be released this week, for clues about the world's biggest economy.

Nearly one-third of Standard & Poors 500 companies will be reporting earnings this week, he said.