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Remy de la Mauviniere, Associated Press
French prime minister Francois Fillon delivers his speech at the opening of the "New World" conference in Paris, Thursday Jan. 5, 2012. More than 300 participants from 18 countries take part in this two-day conference, engaged in direct, real-world dialogue to promote model projects and the best international practices pertaining to four key themes on tomorrow’s Internet: innovation and networks, respect for privacy, bridging digital divides, network security.

PARIS — The specter of Europe's debt crisis returned Thursday after a brief respite, as bank stocks fell sharply on worries about losses on government debt and a French bond auction drew lackluster demand from investors.

Financial stocks slumped across Europe as it became clear banks would have troubled raising billions in new capital in coming months. In Italy, trading in UniCredit shares was halted after they lost a quarter of their value since yesterday morning, when the bank admitted it had to offer huge discounts to new investors to attract capital.

The banks need the money to cover potential losses on government debt, whose value has plummeted across most of Europe in recent months on fear of defaults. Many countries in the region have to roll over billions in debt in coming months, putting huge focus on their bond auctions.

France managed to raise €7.96 billion ($10.31 billion) on Thursday, at the top of its goal, in an auction where demand was solid but far less than at the last sale in December. The borrowing rate for the 10-year bonds, which made up more than half of the auction amount, rose to 3.29 percent from 3.18 percent last time.

The country is under close scrutiny since ratings agencies warned they could strip it of its top AAA grade because of the impact of the crisis and a looming recession on its public finances.

Thursday's bond auction shows investors are still willing to lend to France at good rates, but that they remain cautious. France's banks are burdened with huge amounts of government bonds from weak countries like Greece, and boosting them with state money could be expensive — and possibly trigger a downgrade for France.

Formerly routine affairs, European government bond auctions have become tense ordeals during the crisis. Countries that cannot raise money at reasonable rates must be rescued with bailout packages, and investors have grown concerned in recent months that even countries in the so-called European "core" could join that ignominious club. Thus far, only the relatively small economies of Greece, Ireland and Portugal have sought bailouts.

At the very least, if countries like France are forced to pay more to borrow money, they may become unwilling — or unable — to support their smaller neighbors.

After weeks of watching the bond yields of Italy, France and Spain rise, investors got a small respite this week. Germany and Portugal both sold bonds Wednesday at lower rates than previous auctions.

But France's auction result was not quite so good as those, helping to weaken sentiment in European markets. The euro dropped to $1.2836 — a 15-month low against the dollar.

On the secondary market, where the issued bonds are later traded openly, the yield on French 10-year bonds was stable Thursday at 3.31 percent after the auction.

But yields of Italian and Spanish bonds were on the rise. Both countries are considered too big to bail out, so signs that investors might avoid their bonds are particularly worrying. Italy's yield rose above the psychologically sensitive level of 7 percent — a level which is considered unsustainable in the longer term.

European financial stocks were hit hardest on Thursday. In order to protect banks against losses on government bonds, European governments are forcing them to keep more safe capital on hand. But raising that money has proved tricky for some, since investors are reluctant to buy their stock or bonds.

Italy's largest bank, UniCredit, announced Wednesday that it would offer stock at a 69 percent discount to raise cash — a disturbing sign of just how pressed banks are.

More bad news came Thursday, when the Financial Times reported that Spain's government thinks its banks will have to raise €50 billion more than previously thought. That news sent Spanish bank stocks tumbling and contributed to losses in other countries. France's Societe Generale SA was down 4 percent, for example.

The continued volatility in markets is another sign that investors don't put much stock in the "solutions" unveiled at a summit last month that committed governments to a new treaty that would give European bureaucrats substantial oversight of their budgets.

Leaders hoped to reassure markets that overspending would never again threaten state solvency, but investors have noted that it does nothing to solve the immediate crisis — the heart of which is rising bond yields — and is unlikely to ever be enacted as strongly as it was conceived anyway.

Instead, they want to the European Central Bank step in more forcefully to drive down borrowing costs by buying bonds in the open market, a practice it engages in only modestly right now. Analysts argue that would give governments time to enact longer-term solutions, like restoring credibility in their spending habits and allowing them to invest in growth. For now, governments can only slash spending to woo markets, but that also cripples already anemic growth and threatens to usher in a new recession.

Despite these challenges, French Prime Minister Francois Fillon promised on Thursday that France would invest in growth, by reducing the taxes companies pay on salaries, in the hopes of driving down the unemployment rate, which stands at 9.7 percent ahead of presidential elections this spring.

"What do all of the reports on France's competitiveness tell us today? That the cost of work is too high in our country," he told a conference at the French Finance Ministry.

With mounting government debt, France needs to make the shortfall up somewhere else, and Fillon said it would do so with a new sales tax and by taxing financial transactions.

The latter is controversial since many have argued it will only work if applied across the European Union or even the world. Britain and the U.S. — both of which are major centers of finance — have strongly resisted it.

Fillon vowed France would push ahead.

"It's normal that all sectors participate in a collective effort, including the financial sector," he said.