France has complete faith in the solidity of the U.S. economy and in the U.S. government's determination to implement the Congress's plan, a source close to France's Finance Minister Francois Baroin said on Saturday.

The source, reacting to the downgrading of the United States' credit rating by Standard & Poor's, added that nothing had been decided yet on calling for an early G7 or G20 meeting to discuss the matter.

"We have complete faith in the solidity of the U.S. economy and in its fundamentals and in the determination of the U.S. government to implement the plan approved by Congress," the source said.

The source added that the major challenge for the United States and the euro zone would be to find a balance between debt reduction and economic growth.

It added that French authorities planned to monitor markets "very closely" and were in constant contact with their foreign counterparts.