ATHENS: Greece is set to face mounting pressure from markets looking for aggressive government action to curb the country's overspending in the wake of a credit downgrade and violence in the streets.

The decision by the Fitch agency to downgrade Greece's long-term debt ratings on Tuesday highlighted falling confidence in the country's economic policy, raised the prospect of a crisis budget and increased strains in the eurozone.

The European Commission piled pressure on Greece to clamp down on its ballooning public deficit following the rating downgrade, urging Athens to take additional measures.

"A difficult situation in one euro-area member state is a matter of common concern for the euro area as a whole," said European Union economic and monetary affairs commissioner Joaquin Almunia in a statement.

"It is clear that Greece faces very substantial economic and fiscal challenges ... but more measures are required," he said.

Greece's new socialist government presented its 2010 budget on November 20, but it has failed to impress credit agencies and analysts who said they expected Athens to offer tougher measures within six weeks to give markets confidence.

The proposed budget aims to cut the deficit from 12.7 percent of output to 9.1 percent next year through a wage freeze and a crackdown on tax evasion.

Finance Minister George Papaconstantinou acknowledged Tuesday that the Fitch rating "reflects the lack of credibility that Greece unfortunately acquired over the last few years as well as an extremely difficult economic situation."

The ratings action shook the Greek stock market, which closed down 6.04 percent on Tuesday. Major European stock markets also tumbled, partially over concerns about the debt situation in Greece.

It also widened the spread between the yields of German and Greek bonds to 2.3 percentage points, meaning that Greece has to pay that much more interest than Germany to attract lenders to finance its overspending.

The bad economic news came on the heels of violent protests on Sunday and Monday in the streets of Athens, where stone-throwing youths clashed with riot police over the fatal shooting of a teenager by police 12 months ago.

Government austerity measures could be met by stiff resistance from labour unions, warned analyst David Morrison at GFT, a spread-betting company.

"If the government tries to cut spending and demand wage restraint or job losses in the public sector, they have a very militant workforce to contend with. So, more agitation and unrest to come," he said.

But Greece also has to contend with the expectations of its eurozone peers.

Analysts have warned that the strains in Greece could create the conditions for a crisis on the government bond market in the eurozone.

Recent comments by European Central Bank chief Jean-Claude Trichet point to a "lack of appetite" for ECB support for Greece at this stage, analysts at the Royal Bank of Scotland said.

"Until the ECB hears more aggressive corrective measures from the Greek authorities it is likely to turn a blind eye to the increasing funding cost the country is facing," RBS said.

Trichet said on Monday that Greece was in a "very difficult" situation but that Athens needed to take "courageous" decisions on its budget.

The Fitch decision raised the tone of discussion among analysts about how close Greek bonds now are to a situation in which they are no longer usable by Greek banks as collateral for borrowing money from the ECB.

"The banks are currently able to pledge bonds issued by their government as collateral at the ECB. This will no longer be an option come the end of next year if the other rating agencies follow Fitch's lead," said a note from Capital Economics Ltd.

On Tuesday, Fitch downgraded Greek long-term debt ratings to BBB-plus from A-minus notation, warning that the outlook was negative "given the weak credibility of fiscal institutions and the policy framework."

The agency said that it "understands that further (budget) measures will be announced in January 2010 to support the reduction in the fiscal deficit to 3.0 percent of GDP by 2013."

It said that "increased peer pressure" from within the EU and eurozone was likely "to strongly influence policy choices".

Fitch also downgraded the ratings of five Greek banks later on Tuesday.

On Monday, Standard & Poor's warned that it could downgrade Greece's credit rating, "if we view the government's fiscal assumptions as unrealistic."

"Surely the stakes have just been increased massively," Goldman Sachs analyst Erik Nielsen wrote in a note to investors.

"The Euro-zone will probably welcome this in the hope that Greece will indeed do enough on their budget."