Stock index futures fell on Friday, tracking European equities and the euro as investor worries intensified over the sovereign debt crisis in the region.

Markets also looked ahead to the critical May non-farm payrolls number, which could give insight into the strength of the recovery.

The report is expected to show 513,000 non-farm jobs were added to the U.S. economy, with a big boost from Census Bureau hiring, compared with an increase of 290,000 in April. The data, which could show the biggest monthly gain since September 1983, is due at 8:30 a.m. EDT.

European shares turned negative on bank weakness, led by Societe Generale , as traders cited concern about its derivatives division.

In addition, a spokesman for Hungary's prime minister said the country was at some risk of a Greek-style fiscal crisis.

This adds to the sovereign-debt default fears started by Greece and Spain, said Peter Boockvar, equity strategist at Miller Tabak & Co in New York.

S&P 500 futures fell 9.7 points and were below fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures sank 85 points and Nasdaq 100 futures dropped 19.75 points.

The payrolls data comes a day after a private employment report and weekly jobless claims data showed an improved labor market, though not as much as expected.

The jobs report is a very hyped number and estimates have been going up. So there's more downside risk than upside potential because of it, said Arthur Hogan, chief market analyst at Jefferies & Co in New York.

BP Plc made promising strides in its latest bid to stop the massive oil spill in the Gulf of Mexico and capture oil spewing from a ruptured well. BP's U.S.-listed shares slid 7 cents to $39.20 in premarket trading.

Policymakers from the Group of 20 nations expressed concern Friday about the health of the world economy as they closed ranks behind the euro zone's efforts to tackle a debt crisis that has rattled global markets.

Martek Biosciences Corp reported second-quarter earnings late Thursday that beat expectations and forecast full-year revenues above consensus.

Three top Federal Reserve officials said Thursday it may soon be time to begin raising interest rates as the U.S. economic recovery gathers momentum despite persistently high unemployment.

Wall Street rose for a second straight day on Thursday, with the Nasdaq advancing 1 percent on a late-day surge in technology shares.

(Editing by Jeffrey Benkoe)