LONDON (Reuters) - Oil prices fell toward $61 (S$88) a barrel on Monday, giving away some of last week's gains, ahead of OPEC's meeting in Vienna, where the group was widely expected to agree not to cut oil output further.

U.S. crude futures for July delivery fell 62 cents to $61.05 a barrel by 1100 GMT (7:00 a.m EDT).

London Brent crude U.S. markets are closed on Monday for the Memorial Day holiday. NYMEX floor trading resumes on Tuesday.

Oil prices rallied around 9.5 percent last week, boosted by a spate of U.S. refinery problems and unrest in major oil exporter Nigeria, and are nearly double the lows they hit in December on speculation the economic recession is easing and demand for energy will revive.

Nigeria's main militant group said on Monday it had attacked major oil pipelines in the Niger Delta to prevent five flow stations feeding a facility run by U.S. Chevron from operating, but there was no independent confirmation.

Ministers from the Organization of the Petroleum Exporting Countries (OPEC) were expected to make no change to oil supply when they meet in Vienna on Thursday as higher prices helped mitigate their concerns about overflowing fuel inventories and dwindling demand.

Saudi Arabian Oil Minister Ali al-Naimi said OPEC would "probably stay the course" as he forecast a pick-up in demand and prices eventually rising toward $75 a barrel.

Iran's OPEC governor said the possibility of OPEC agreeing to cut oil output again at its May 28 meeting was remote, an Iranian newspaper reported on Monday.

In recent days, Khatibi has made clear his view that production should be reduced again due to rising oil stocks.