Moody's downgrade of Portugal's bond ratings to 'Baa1' from 'A3' on Tuesday also brought the euro zone debt crisis back at the forefront of investors' minds.
Late on Monday, Federal Reserve Chairman Ben Bernanke said a recent rise in US inflation was driven primarily by rising commodity prices globally, and is unlikely to persist.
Bernanke's comments were in sharp contrast to recent comments made by a string of US central bank officials, some of whom have argued the time was coming for the Fed to begin tightening monetary policy.
Investors awaited the release of the Federal Open Market Committee's minutes from its meeting of March 15, due at 1800 GMT on Tuesday, to get more insight on the outlook for US interest rates.
Earlier on Tuesday, Australia's central bank kept interest rates steady for a fifth month, saying a lofty Australian dollar, moderate wages growth and intense retail competition would help keep inflation at bay for the year ahead.