NEW YORK (TheStreet) -- Stock futures were modestly lower, following European markets into the red as Greece debt talks continued with no clear resolution in sight. 

S&P 500 futures fell 0.15%, Dow Jones Industrial Average futures slipped 0.12%, and Nasdaq futures slid 0.18%. 

European markets were lower after Greece submitted its latest list of reforms to creditors, though sources have told Reuters that the plan offers no major new concessions. Leaders of Germany, France and a number of Greece's other international creditors said on Monday that they would work with "real intensity" to seal a deal to prevent Athens from defaulting. 

"We have submitted a realistic plan for Greece to exit the crisis," Greece's Prime Minister Alexis Tsipras told reporters. "A realistic plan, whose acceptance by the institutions, our lenders and our partners in Europe will mark the end of the scenario of divisions in Europe."

Trouble in Greece is reaching a boiling point as the debt-ravaged country faces a repayment to the International Monetary Fund on Friday of 300 million euros ($329 million). In total, Greece needs to repay the IMF nearly 1.6 billion euros ($1.75 billion) this month. 

Dollar General (DG) added nearly 3% in premarket trading after beating analysts' quarterly estimates on its bottom line. The discount retailer earned 84 cents a share in its first quarter, 3 cents higher than expected, while same-store sales rose 3.7%. 

Medtronic (MDT) added 1% after a better-than-expected fourth quarter. The medical equipment developer earned $1.16 a share, a nickel above estimates, while revenue of $7.3 billion surged 59.7% from a year earlier. 

Plug Power (PLUG) jumped 4.5% after the alternative fuel-cell developer announced an expansion contract with Wal-Mart (WMT) Canada to provide 124 GenDrive fuel cells to its Alberta distribution center. 

Apple (AAPL) is reportedly nearing the launch of a new subscription music-streaming service, according to The Wall Street Journal. The tech giant will likely unveil the revamped Beats Music service at the June 8-12 WWDC conference. 

Ford (F) and General Motors (GM) were on watch ahead of their monthly car sales reports out later this morning. TrueCar estimates the average U.S. automobile transaction price rose 4% in May. 

Wal-Mart will reportedly begin a second phase of wage hikes in July, according to The Associated Press. The first phase increased average hourly rates to $13 an hour. 

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