Just five days after European authorities unleashed a €159 billion (£141 billion) aid package designed to prop up the eurozone, Spanish and Italian bond yields soared on concerns over sovereign debt. Spain’s short-term cost of borrowing hit three-year highs. At an auction of Spanish government debt demand fell, while yields at a sale of six-month Italian paper hit their highest since late 2008. By late afternoon, the yield on Italian 10-year bonds dropped back from 5.72pc to 5.63pc as Italy cancelled a debt auction scheduled for August. Traders said the move “provided some relief” to volatile markets. Spanish bonds also dropped to 5.96pc having hit 6.07pc earlier. But the price of German Bunds, the benchmark of the eurozone debt market, was back up to levels seen before the aid package. Traders said the markets were now unconvinced that the authorities have done enough to prevent a meltdown of the euro. Marc Ostwald, from Monument Securities, said: “The most important point again is the fact that relative to the last auction yields are much, much higher. It shows we may have had some relief last week but that relief has proven to be rather short-lived.” Christine Lagarde, the new boss of the International Monetary Fund, said the uncertainty was the result of the complexity of the bail-out agreement. She added markets were nervous because of the questions the authorities had left unanswered. Last week the 17 members of the eurozone agreed a bail-out package for Greece. Lower interest rates on loans from the European Financial Stability Facility were also opened as an option for Portugal and Ireland, which have also received rescue packages. Meanwhile, Greece said it will invite bids for a multi-billion euro retail project at Athens’ old airport in September. The sale of the area around Hellenikon – which the Qataris looked at buying for €7bn – will be one of the first big auctions in Greece’s attempt to raise €50bn from state assets by 2015. The asset sales, which are highly unpopular in Greece, are a key condition of the international bail-outs.