Associated Press
Pope Benedict XVI, white figure sitting on the stage, celebrates his last general audience in St. Peter's Square, at the Vatican, Wednesday, Feb. 27, 2013. Benedict XVI basked in an emotional sendoff Wednesday at his final general audience in St. Peter's Square, recalling moments of "joy and light" during his papacy but also times of great difficulty. He also thanked his flock for respecting his decision to retire. (AP Photo/Alessandra Tarantino)

ROME — Why has Italy's muddled election result spooked global investors so much? Because it raises unsettling questions about the availability of the financial safety net that has kept Europe from catastrophe for the past six months.

That safety net is a crucial offer from the European Central Bank to buy unlimited quantities of struggling countries' bonds. The one catch was that participating countries had to commit to austerity measures — such as spending cuts and tax increases to lower their deficits.

And if there's any clear message from the Italian elections, it's that voters rejected austerity.

If Italy can't — or won't — agree to cuts and reforms to promote stronger growth, the ECB can't help.

That would leave Italy defenseless if its borrowing costs rise to unmanageable levels and into default territory. And if Italy fails, Europe can't afford to bail it out.

A top European Central Bank official underlined Wednesday that any country that wants to use the crucial backstop will have to meet stiff conditions and agree to take steps to cut its deficit.

Peter Praet, the top ECB official in charge of its economic analysis and forecasts, did not mention Italy in the text of his speech in Frankfurt. But he warned that the bond-purchase shield "will only be activated in cases where the benefiting country has signed up to strict and effective conditionality," meaning an agreement to take concrete steps to curb its financial problems.

Praet's warning came as Italy saw its borrowing costs rise as it sold $8.5 billion of 10-year and five-year bonds. The interest yield rose to 4.83 percent from 4.17 percent a month ago for the 10-year and to 3.59 percent from 2.94 percent for the five-year.

So far, Italy's borrowing costs have risen only moderately. But the fear is that continuing turmoil could let them climb toward the heights of late 2011 and early 2012 — a hefty 7 percent.

The ECB bond purchase program has been given most of the credit for the easing of the eurozone debt crisis in recent months. Before the ECB offered Sept. 6 to buy unlimited amounts of government bonds issued by a struggling country, Italy and Spain faced borrowing costs that would have proved crippling in the long term. The fear was that these two big economies — the third- and fourth-largest among the 17 European Union countries that use the euro — would be pushed into defaulting on their debts.

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No bonds have been bought under the ECB plan, but the mere offer reassured investors and sent borrowing costs lower for debt-plagued countries such as Italy and Spain.

"Basically, investors are taking this on faith," said Simon Tilford, chief economist at the Center for European Reform in London.

The Italian result risks undermining that faith.

"It would be very hard for the ECB to wade into the market and buy substantial quantities of Italian debt if there is political gridlock in Italy and a broad based rebellion against the austerity strategy," Tilford warns.