Also spurring trade was the weekend announcement of AT&T's plan to take over T-Mobile USA in a $39 billion deal that would make AT&T the country's largest cellphone carrier.

The Dow Jones Industrial Average picked up 186.29 points (1.57 percent) to 12,044.81 in the first 15 minutes of trade.

The broader S&P 500 was up 17.99 (1.41 percent) at 1,297.19, while the tech-heavy Nasdaq Composite rose 44.58 (1.69 percent) to 2,688.25.

"The US equity markets are nicely higher in morning action, beginning the week on a positive note, led by a major M&A announcement in the telecom sector and some relative optimism of progress in Japan's ability to avoid a nuclear meltdown," said analysts at Charles Schwab.