Italy and Spain had to pay much more to auction 7.6 billion euros of debt on Tuesday, reflecting market unease about the future of the central bank monetary stimulus that has fanned global demand for riskier assets.

Rome's two-year borrowing costs jumped to their highest level since September 2012, more than doubling what Italy paid at the most recent comparable auction.

Madrid's short-term funding costs leapt to 6-month highs at a double-bill sale which, however, saw solid demand.

Until the end of May, peripheral euro zone bonds had basked in a 10-month rally fueled by a European Central Bank pledge to buy bonds of weaker euro zone economies if needed, and by money printing by central banks around the world.

But the U.S. Federal Reserve clearly signaled last week it would begin scaling back its bond-buying program soon, sparking an investor exodus from riskier markets and making it harder for the euro zone's weaker states to service their debt.

Spain's Economy Minister Luis de Guindos said an uncontrolled removal of monetary stimulus could derail a global economic recovery.

ECB President Mario Draghi sought on Tuesday to reassure markets, saying the euro zone central bank was nowhere near exiting its accommodative monetary policy

But what investors fear is that when the pullout comes, it will be too early for the states in the currency bloc that are still struggling to pull their economies out of recession.

"While it's premature to talk about a renewed flare-up of the bond market crisis in the euro zone, funding pressures in Spain and Italy are resurfacing at a time when the two economies can ill-afford higher borrowing costs," said Nicholas Spiro, managing director at Spiro Sovereign Strategy.

After the $9.9 billion sales, Spain's benchmark 10-year bond yields rose on the secondary market just above 5 percent and the rate on Italian 10-year bonds was back to 4.83 percent, both roughly a full percentage point higher than the lows reached in May.

REAL ECONOMY IN FOCUS

Less monetary stimulus will most likely bring economic fundamentals back in focus, which yield-hungry investors have neglected for so long.

On Tuesday, Rome sold 3.5 billion euros of new zero-coupon bonds at a yield of 2.40 percent. A month ago it paid 1.11 percent, a euro-lifetime low, to sell zero-coupon bonds of a maturity that was six months shorter.

"The result of the sale, with a sharp rise in the yield and a fall in demand, underscores the growing fears about the adverse consequences of a withdrawal of liquidity," said Spiro.

The head of Italy's Debt Management Office said on Monday the Treasury will have to cope with choppy markets for as long as the euro zone economy gives no signs of improvements.

What can give a helping hand to both Rome and Madrid is the fact the two countries have frontloaded their funding for 2013, rating agency Standard and Poor's said on Tuesday.

"With all the movement that we have seen over the last fortnight or so ... we are far away from the red danger zone where we were last summer for example," Moritz Kraemer, S&P's head sovereign analysts for EMEA, said.

Spain's 10-year debt costs reached a high of over 7.6 percent last July, while Italy's yields stood around 6.60 percent.

"A lot of those countries have done a lot of pre-funding so there is no immediate threat to it," Kraemer said.

Italy has so far shifted more than 60 percent of this year's medium- and long-term funding target and Spain around two thirds of its medium-term debt goal.

Rome will return to the market on Wednesday to offer 8 billion euros of six-month bills while on Thursday it will put on sale up to 5 billion euros of long-term bonds.

Investors will also keep a careful eye on Italy's volatile political backdrop, after former prime minister Silvio Berlusconi was handed a seven-year jail sentence on Monday for abuse of office and paying for sex with a minor.