Monday also marks the unofficial start of first-quarter earnings season, with aluminum producer Alcoa(AA) on tap to report results after the closing bell.
In other corporate news, General Electric(GE) said it planned to buy energy company Lufkin Industries(LUFK) for $3.3 billion. Shares of Lufkin, which builds and maintains equipment for oil and gas wells, surged in premarket trading.
Anheuser-Busche InBev's(BUD) proposed $20 billion acquisition of Mexican brewer Grupo Modelo appears to be back on track after the companies, along withConstellation Brands(STZ) and Crown Imports, said they'd reached an agreement that would settle the Justice Department's objections to the deal.
In Europe, Portugal's top court invalidated a portion of the government's austerity package on Friday, leaving policymakers scrambling for additional revenue to comply with the terms of the country's international bailout.
Portuguese stocks fell but the main European markets were slightly higher in midday trading. London's FTSE 100 and the DAX in Frankfurt edged up about 0.3%, while the CAC 40 in Paris rose 0.7%.
Meanwhile, the Nikkei continued to rally, adding another 2.8%, as investors cheered new stimulus measures from the Bank of Japan. The yen weakened against the U.S. dollar, falling to its lowest level since 2009.