GLOBAL MARKETS-Shares rise on optimism before U.S. jobs data; oil falls

* Drop in U.S. jobless claims fuels optimism

* Traders eye U.S. March nonfarm payrolls data

* Oil slips as Iran talks back in focus

* U.S. dollar falls ahead of U.S. jobs data (Adds oil settlement prices)

By Sam Forgione

NEW YORK, April 2 (Reuters) - U.S. stocks snapped back on Thursday after two sessions of losses, as a fall in jobless claims increased optimism ahead of a key payrolls report, while oil tumbled on fears of worsening oversupply if sanctions over Iran's nuclear program are dropped.

Data showing an unexpected fall in the number of Americans filing new claims for unemployment benefits boosted sentiment before the U.S. Labor Department's nonfarm payrolls report for March, which will be released on the Good Friday holiday.

U.S. and European stock markets will be closed on Friday. Economists polled by Reuters expect a gain of 245,000 jobs, down from 295,000 in February.

Trading could become volatile as participants position for Friday's data. Weak payrolls would not necessarily spook Wall Street, however, since a below-consensus jobs number could ease concerns over a nearer-term Federal Reserve interest rate rise.

"People are looking ahead to the jobs report, and right now it would be a surprise if it was weaker than expected," said John Carey, portfolio manager at Pioneer Investment Management in Boston.

Oil prices fell as much as 5 percent as Iran and world powers reached a preliminary pact on Tehran's nuclear program, but pared losses after officials said talks for a final agreement will continue through June. Tehran is hoping for a deal that will end crippling economic sanctions and allow it to sell millions of barrels of oil.

A measure of equity indexes worldwide rose, boosted by gains in U.S., emerging markets and Japanese shares. European shares slipped after Greece's lenders said the country needed to do more to unlock financial aid.

MSCI (NYSE: MSCI - news) 's all-country world index was last up 0.71 percent at 427.57, while its emerging markets index gained 1.32 percent to 995.95. The FTSEurofirst index of 300 leading European companies closed down 0.20 percent at 1,586.76.

The Dow Jones industrial average was last up 0.27 percent at 17,746.53. The S&P 500 was up 0.3 percent at 2,065.84. The Nasdaq Composite was up 0.09 percent at 4,884.45.

Brent crude settled down $2.15, or 3.8 percent, at $54.95 a barrel. U.S. crude settled down 95 cents, or 1.9 percent, at $49.14 a barrel.

Prices of safe-haven U.S. Treasury debt slipped. Benchmark 10-year Treasury notes were last down 10/32 in price to yield 1.9 percent, from a yield of 1.87 percent late on Wednesday.

The dollar slipped against major currencies despite the strong U.S. data, as traders took profits from bullish dollar positions ahead of the jobs report, which could lead to volatile trading on thin volumes in the currency market.

Thursday's unemployment data, "after disappointments, will help the dollar, but the focus is still on Friday's jobs report," said Vassili Serebriakov, currency strategist at BNP (Paris: FR0000131104 - news) Paribas in New York.

The dollar index, which measures the greenback against a basket of six major currencies, was last down 0.73 percent, at 97.465. U.S. gold for June delivery slipped $7.30 an ounce to settle at $1,200.90. (Reporting by Sam Forgione; Additional reporting by Lionel Laurent in London and Daniel Bases and Ryan Vlastelica in New (KOSDAQ: 160550.KQ - news) York; Editing by James Dalgleish and Jonathan Oatis)