NEW YORK (TheStreet) -- Stock futures pulled back from Monday's rally as crude dropped below $48 a barrel in anticipation of key developments in Iran.

S&P 500 futures were down 0.39%, Dow Jones Industrial Average futures slid 0.46%, and Nasdaq futures fell 0.43%. All benchmark indexes added more than 1% on Monday and, if no gains are forthcoming on Tuesday, will likely close out the month with losses. 

Crude oil prices dropped lower as commodity traders focused on stalled negotiations between Iran and six world powers over a nuclear deal. If passed as proposed, Iran will be restricted from developing nuclear weapons in exchange for the lifting of economic sanctions. Easing sanctions would mean the release of Iranian oil onto an already-oversupplied global commodity market. 

Leaders have given themselves a 6pm EST deadline on which to agree on a preliminary nuclear deal. West Texas Intermediate crude fell 2.1% to $47.68 a barrel. 

European markets were lower after eurozone unemployment came in higher than expected at 11.3% in February, compared to forecasts of 11.2%. The consumer price index came in slightly better, narrowing declines to 0.1% year on year in March from 0.3% in February.

Germany's economy remained head-and-shoulders above the broader region. Unemployment fell to a record low of 6.4% in March, while retail sales in February climbed 3.6%. 

Germany's DAX fell 0.71%, France's CAC 40 slid 0.73%, and the FTSE 100 in London tumbled 1.1%. 

The U.S. dollar continued to climb against other major international currencies, looking to close out its best quarter since 2008. The euro headed for its worst quarter on record, down around 11% since January as the euro zone and U.S. diverge in monetary policy. 

IBM (IBM) - Get Report moved slightly lower after announcing it will invest $3 billion over the next four years building an "Internet of Things" unit. The division will aim to develop technology to gather and analyze real-time data. 

Amazon (AMZN) - Get Report inched lower after its rumored acquisition target Net-a-Porter announced a merger with Italian fashion site Yoox. Net-a-Porter parent Richemont will receive 50% of the combined group. 

Charter Communications (CHTR) - Get Report surged nearly 10% after Reuters reported it has agreed to purchase Bright House Networks for around $10.4 billion. Bright House has approximately 2.5 million cable subscribers. 

Philips (PHG) - Get Report slid nearly 2% after agreeing to sell an 80.1% stake in its lighting division to Go Scale Capital for $2.8 billion. 

On the economic calendar, the S&P Case-Shiller 20-city home price index is expected to show a slight improvement from December. Business activity in the Chicago region is expected to have improved over March in the latest Chicago PMI figures. The Conference Board's consumer confidence index is forecast to recover close to nearly 8-year highs reached earlier this year.