In a statement, Sarah Carlson, Moody’s lead analyst for Greece, said it was “unlikely that the rating will remain at A3, unless the government’s actions can restore confidence in the markets and counteract the prevailing headwinds of high interest rates and low growth.”

The stream of news pushed the yields on Greek bonds up to new highs — to 8.835 percent, above the 8.529 percent return that investors currently demand for similar debt from South Africa.

Image Demonstrators scuffled with police in Athens on Thursday. Credit... Louisa Gouliamaki/Agence France-Presse -- Getty Images

The euro slid in early Asian trading on Friday to $1.3201 against the dollar, the lowest level in a year. On Thursday in Europe, it dropped to $1.3316, down from $1.3401 on Wednesday. Shares in Athens also tumbled again on Thursday, with the benchmark index closing almost 4 percent lower, taking its losses for the year so far to more than 15 percent.

Officials in Athens and Brussels sought to limit the damage.

The Greek Finance Ministry said in a statement that the announcement by Eurostat did not alter its goal of reducing the deficit by at least four percentage points of G.D.P. in 2010, as laid down in the Greek stability and growth program, which it forwarded to the European Commission for scrutiny.

“The government has already adopted all the necessary measures — in excess of 6 percent of G.D.P. — to ensure the achievement of this objective and is rapidly progressing on the implementation of all policy and structural changes,” it said.

Analysts expressed concern that the increased debt and deficit forecasts could spread the economic pain further into the future.