Spain sold 3.5 billion euros ($4.47 billion) of 15-year bonds through banks as Prime Minister Mariano Rajoy bids to convince investors he can pull the economy out of a six-year slump.

The nation sold the 5.15 percent securities maturing in October 2028 to yield 280 basis points over mid-rate swaps, according to data compiled by Bloomberg. The sale was managed by Banco Bilbao Vizcaya Argentaria SA, BNP Paribas SA, CaixaBank SA, Credit Agricole Corporate & Investment Bank, Credit Suisse Group AG and Societe Generale SA.

“It’s actually quite a decent result and an encouraging signal,” said Michael Leister, an interest-rate strategist at Commerzbank AG in London. “To be fair, it’s the first ultra-long Spanish deal since 2011 so clearly this wasn’t going to be an easy sale.”

Spain’s Treasury said in May it would consider selling 15-year bonds through banks as well as offering index-linked and dollar-denominated debt after borrowing costs fell in response to a European Central Bank pledge to defend the euro. Today’s sale is the longest maturity that Spain has sold through banks since November 2011, data compiled by Bloomberg show.

“This shows markets’ confidence in Spain and the political stability of Spain,” Economy Minister Luis de Guindos told reporters in Brussels. The country has now covered almost 70 percent of its funding program for this year, he said.

The International Monetary Fund said today it expected Spain’s economy to stagnate next year after shrinking 1.6 percent in 2013. The IMF previously predicted growth of 0.7 percent this year.

Spanish officials led by Rajoy have said the economy is at a turning point and will return to growth starting this quarter.