The prime minister of France, the biggest economy hit by the downgrade, vowed to press ahead with cost-cutting measures that opponents say will suffocate growth. The loss of its coveted AAA status wounded France's self-image and market credibility just as it's facing a new recession and presidential elections.
The move Friday night may make it more expensive for struggling countries to borrow money, reduce debts and sustain growth. It also came just as crucial negotiations between the Greek government and its private creditors appeared close to collapse.
Voices rose up Saturday against the power that ratings agencies wield. Critics of S&P have questioned its credibility and relevance before because it failed to foresee the collapse in the U.S. subprime mortgage market, which helped trigger the financial meltdown of 2008.
The latest downgrade brought a downbeat end to a mildly encouraging week for Europe's most debt-laden nations. It also served as a reminder that the 17-country eurozone faces what German Chancellor Angela Merkel called a "long road" ahead to win back investors' confidence.
Cyprus President Dimitris Christofias called the downgrade "unacceptable."
"The latest downgrade is completely unfair and loaded with ulterior motives," he told reporters. "Just when the Cyprus economy is breathing easier and showing signs of emerging from the crisis, and when our financing needs for 2012 and perhaps beyond 2012, have been covered, a (credit ratings) agency comes along to downgrade."
Austria's chancellor criticized S&P's decision to strip his country of its AAA rating, and noted that his coalition government is working on an austerity package.
Werner Faymann wrote on his Facebook page that the decision showed "that Austria must become more independent from the financial markets."
In Germany, whose AAA rating remained untouched, a senior lawmaker with Merkel's conservative party, Michael Meister, suggested action to reduce the significance of ratings. Merkel signalled her support.
Germany's foreign minister called for independent European ratings agencies instead of relying solely on the leading, U.S.-based agencies such as Standard & Poor's.
And Vice Chancellor Philipp Roesler, who is also the economy minister, was quoted as telling the weekly Der Spiegel, "It is apparent time and again that U.S. rating agencies pursue very much their own goals."
It's unclear though whether a European agency would come to different conclusions or reduce what critics see as a disproportionate influence that ratings agencies have on markets and policymakers.
S&P spokesman Martin Winn dismissed suggestions that the agency's decisions were political and could further hurt indebted countries. "The track record of our sovereign ratings as indicators of default risk worldwide is very strong," he told The Associated Press.
S&P analyst Moritz Kraemer said in a conference call Saturday that European government measures aren't sufficient to restore confidence.
"They have not achieved a solution that is sufficient in size or scope," he said. He added that austerity measures require "huge sacrifices" of the public that might prompt a backlash.
In Romania on Saturday, residents staged a third day of protests against the government over cost-cutting and falling living standards.
In Paris, demonstrators chanted in front of the S&P French offices and castigated the government for paying so much heed to the ratings agencies.
"The French people know what their value is and we don't need ratings agencies to tell us what we are worth," said Raquel Garrigo, spokesman for the Left Front political party.
Merkel and French Prime Minister Francois Fillon said the downgrades should push European countries to quickly implement a planned pact to strengthen budget discipline.
Germany and France have piloted rescue efforts for other eurozone countries as the continent has been swept up in crisis after crisis over the past two years. The downgrade, by pushing up France's borrowing costs, could make it harder for France to help others.
Merkel sought to allay concerns that the downgrade of France would complicate the work of the bloc's temporary rescue fund, the €440 billion ($560 billion) European Financial Stability Facility. However, she underlined the urgency of putting its permanent successor, the European Stability Mechanism, in place quickly.
Fillon said France's government wouldn't adjust this year's budget yet, because it had been devised with an assumption of higher borrowing costs. S&P had warned 15 European nations in December that they were at risk for a downgrade, and Moody's has France and other European governments on review.
Standard & Poor's stripped France of its coveted AAA status, knocking it down one notch to AA+, the level of U.S. long-term debt after S&P downgraded it last summer. It dropped Italy even lower. Germany retained its top-notch rating, but Portugal's debt was consigned to junk.
Stocks fell Friday as downgrade rumours reached trading floors, but the declines were nothing like the wrenching swings of last summer and fall.
The prime minister of Spain — also downgraded — promised to reduce the budget deficit by reining in public spending. In his first major speech to Popular Party members as premier and party leader, Mariano Rajoy described "living a difficult moment."
France's presidential elections could complicate Europe's discussions. President Nicolas Sarkozy, who has been at the heart of the debate, is highly unpopular and far from certain of winning a second term.
The man who tops polls ahead of the April and May elections, Socialist Francois Hollande, said the downgrade was a punishment for conservative Sarkozy's policies.
Geir Moulson in Berlin, Cecile Brisson and Jeffrey Schaeffer in Paris, Menelaos Hadjicostis in Nicosia, Cyprus, and Harold Heckle in Madrid contributed to this report.