Oil falls nearly 4 percent after tentative nuclear deal for Iran

(Reuters) - Brent oil fell nearly 4 percent on Thursday after a preliminary pact between Iran and global powers on Tehran's nuclear program, even as officials set further talks in June and analysts questioned when the OPEC member will be allowed to export more crude.

Traders had been fixated on the talks held in Lausanne, Switzerland for over a week as Iran tried to agree with six world powers on concessions to its nuclear program to remove U.S.-led sanctions that have halved its oil exports.

The sanctions against Iran will come off under a "future comprehensive deal" to be agreed by June 30, after it complies with nuclear-related provisions, Iranian Foreign Minister Javad Zarif told a news conference.

"If nothing is going to be signed until June, something could go wrong between now and then," said Phil Flynn, analyst at Price Futures Group in Chicago.

Bob McNally, an adviser to former U.S. president George Bush who heads energy research firm Rapidan Group, noted Iran will need much patience as the "sanctions are not likely to be lifted until late 2015 or early 2016, though we could see slippage beforehand."

North Sea Brent crude futures, the more widely-used global benchmark for oil, settled down $2.15, or 3.8 percent, at $54.95 a barrel, almost $1 above the session low.

U.S. crude futures settled down 95 cents, or 2 percent, at $49.14 a barrel, after falling nearly $2 earlier.