World stocks as measured by MSCI index gained 0.9 percent.
European equities pared earlier gains after China's central bank raised lenders' required reserve ratios. Europe's FTSEurofirst 300 climbed 0.5 percent.
Oil fell from earlier highs after Libya declared a cease-fire in the country to protect civilians and comply with a United Nations resolution passed overnight.
"That (Mideast unrest) quiets down and Japan quieting down will lead to buying," said Stephen Massocca, managing director at Wedbush Morgan in San Francisco.
Brent crude had surged above $117 a barrel on worries of escalating unrest in oil-rich countries after the United Nations approved military action to contain Libya's Muammar Gaddafi. Brent crude for May delivery slipped 16 cents, or 0.1 percent to $114.74 a barrel after the cease-fire. US crude was little changed at $101.51.
The UN Security Council passed a resolution endorsing a no-fly zone for Libya. It authorized "all necessary measures" to protect civilians against Gaddafi's forces.
The dollar climbed nearly 3 percent to 81.07 yen, retreating from a session high of around 81.98 yen, following the G7 announcement, which came just as the Tokyo stock market opened.
The show of solidarity by the G7 major developed economies to support Japan through its biggest crisis since World War Two comes a day after the yen soared to a record 76.25 per dollar in chaotic trading. It is the first coordinated currency intervention by the G7 in a decade.
The G7 "is just helping sentiment, and stocks sensitive to risk will push on. But optimism is going to be guarded as there are no firm resolutions surrounding the Japanese nuclear crisis and the Middle East, and anything can happen on the weekend," said Giles Watts, head of equities at City Index in London.
The Dow Jones industrial average gained 110.72 points, or 0.94 percent, to 11,885.31. The Standard & Poor's 500 Index was up 9.67 points, or 0.76 percent, at 1,283.39 and the Nasdaq Composite Index was up 10.78 points, or 0.41 percent, at 2,646.82.