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A pledge by Japan to support Europe’s bailout efforts helped ease the pressure on European markets Tuesday despite speculation that Portugal will soon have to join Greece and Ireland in getting bailed out.

Portugal insisted it doesn’t need a bailout and criticized its European partners on Tuesday for not doing enough to shield the euro from a debt crisis that has already forced Greece and Ireland to seek outside help.

Disagreement over how to fight Europe’s debt crisis deepened as leaders headed into a two-day summit in Brussels and uncertainty fueled investors’ concerns once again

The dollar remained under pressure following a warning from a leading credit rating agency that the U.S. could have a negative outlook put on its triple-A rating if it doesn’t get a handle on its borrowing over the coming two years.

Global stocks were mixed Monday after U.S. Federal Reserve chairman Ben Bernanke said the Fed might buy more bonds, while a stronger yen weighed on Japanese exporters.

The European Central Bank’s chief says the euro remains a "credible" currency despite the debt crisis that has required the bailouts of Ireland and Greece and raised worries about the future of the shared currency.

Investors sold off government bonds from Spain, Portugal and Italy on Tuesday amid worries that Europe’s debt crisis has not been contained by Ireland’s bailout but is putting pressure on other fiscally weak countries.

The 16-nation euro currency will survive the debt crisis, German Chancellor Angela Merkel vowed Thursday, and a senior central banker said the European Union would be willing to increase its €750 billion ($1 trillion) bailout fund if necessary.

Nervous bond markets pressed Portugal and Spain on Tuesday amid concerns they are the next weak links in Europe’s debt crisis now that Ireland has accepted a massive loan to prop up its banks.

World stock markets fell Wednesday amid mixed corporate earnings and on views that the U.S. Federal Reserve’s expected stimulus measures will be more modest and gradual than expected.