In late afternoon trading in New York, the Dow Jones Industrial Average gained 1.13 per cent, the Standard & Poor's 500 Index rose 1.38 per cent, while the Nasdaq Composite Index advanced 1.45 per cent.
"People are anticipating some type of response from the Fed tomorrow and are buying or covering shorts in anticipation of that," Paul Zemsky, head of asset allocation at ING Investment Management in New York, told Reuters. "There's a risk the market gets disappointed."
In Europe, optimism prevailed that the risk of a Grexit from the euro is declining rapidly.
The Stoxx 600 Index climbed 1.6 per cent for the day, while the euro strengthened, rising 1.2 per cent to US$1.2720 and advancing 1 per cent to 100.44 yen.
Greek parties promised to form a coalition government soon - Pasok leader Evangelos Venizelos told reporters today that a new Greek government could be ready by midday tomorrow - as the country's European creditors prepare to loosen the conditions of the financial rescue.
A first step will be when Greece's still to-be-formed government asks for changes to the 240 billion-euro bailout programs, leading to a revision of economic-performance targets sometime before September, a European official told reporters in Brussels today, according to Bloomberg News.
Even so, trouble remains including in Spain which today had to pay 5.07 per cent to sell 12-month Treasury bills and 5.11 per cent to sell 18-month paper. Yields on longer-term bonds remain above 7 per cent as investors worry about the extent of the financial assistance this debt-laden euro zone member will need to help restore the health of its banking system, and rein in the government's budget deficits.
"The decidedly elevated yield levels leave a question mark firmly in place as regards the sustainability of Spain's public finances while doing nothing to temper speculation as to how long the country might hold out before looking for a more comprehensive bailout," Rabobank strategist Richard McGuire told Reuters.