Spain's borrowing costs shot up at a bond auction on Thursday, after economic data confirmed the country is back in recession and reports of an outflow of deposits from nationalized Bankia hammered its share price.
The Spanish Treasury had to pay around 5 percent to attract buyers of three- and four-year bonds. The longer-dated paper sold with a yield of 5.106 percent, way above the 3.374 percent the last time it was auctioned.
"This ... fits the pattern of recent sales, with the Spanish treasury successfully getting its supply away but at ever-higher yields," said Richard McGuire, rate strategist at Rabobank in London.
"This unfavorable trend looks set to remain firmly in place ... Ultimately, this ratcheting up of yields will likely require some form of outside intervention," McGuire said.
Spanish Prime Minister Mariano Rajoy said on Wednesday his government, struggling to reduce its budget deficit, could soon find it difficult to fund itself affordably on the bond market unless the pressure eases.
His finance minister, Cristobal Montoro, meets heads of finance of all 17 regions later to review their budget plans which are a crucial plank of the drive to lower public debt.
The European Commission warned last week that stubbornly high debts in the regions and the welfare system would prevent Spain meeting its deficit goal of 5.3 percent of GDP this year.
Spain's 10-year yields have spiked back above 6 percent, which investors view as a pivot point that could accelerate a climb to 7 percent, a cost of borrowing widely seen as unsustainable even though Madrid has sold well over half its debt needs for the year.