Two U.S. Federal Reserve officials said on Monday that the euro zone debt crisis has added some uncertainty to the economic outlook but the impact is not yet big enough to influence the interest rate policy of the United States.

The heads of the Chicago and Philadelphia reserve banks, neither of whom have voting rights on the Fed's interest rate-setting panel, said they were cautiously optimistic that the world's largest economy would remain on course for a sustained recovery despite the euro zone crisis.

The situation in financial markets in Europe does add uncertainty, but at the moment I look for the recovery in the U.S. to continue to improve and I don't see any changes in my outlook at the moment, Chicago Federal Reserve Bank President Charles Evans told reporters.

He said the recent rise in the unemployment rate was because more people had resumed their search for jobs, which he said was an indication of growing optimism.

Charles Plosser, president of the Philadelphia Federal Reserve Bank, said the U.S. economy was not likely to encounter a double-dip.

I don't anticipate at this point that the United States in particular will see a double-dip, but obviously the financial turmoil in Europe raises some clouds on the horizon that we need to be cautious about.

Plosser said he saw no developments in the euro zone situation significant enough to force the U.S. central bank to change its policy.

The two officials were speaking on the sidelines of an international seminar hosted by South Korea's central bank.

(Reporting by Yoo Choonsik; Editing by Chris Lewis)