The Dow Jones Industrial Average was up 72.51 points (0.56 percent) to 12,909.84 in the first five minutes of trade.

The broad-based S&P 500 added 9.66 (0.71 percent) to 1,362.29, while the tech-rich Nasdaq Composite rose 19.44 points (0.66 percent) to 2,955.13.

"Global equity markets are rallying in front of the deadline for the private-sector involvement in the Greek debt swap plan, reflecting an expectation that the deal will get done and that a disorderly default will be avoided," said Briefing Research.

Markets appeared unbothered by a rise in US weekly jobless claims, since the pickup did not change the overall picture of an improving jobs market in the country.

Also underpinning the buying were the decisions by the European Central Bank and the Bank of England to hold their key lending rates steady.