The Portugese debt agency raised 1.05 billion euros over 18 months at 1.603 percent, up from 1.506 percent at a similar sale in March, with demand for the bills about twice the offer.

The agency also raised 450 million euros over six months at 1.041 percent, up from 0.811 percent a month ago with demand 2.5 times greater than the offer.

The rates were in line with secondary markets worldwide, said Filipe Silva, fixed income strategist at Banco Carregosa.

“In the past few weeks, the trend has been for higher rates on all sovereign debt, including (safe-haven) Germany. This is due mainly to the rumours of an end to stimulus by central banks around the world.”

“This is not a movement specific to Portugal,” he added.

International investors have been speculating about when the US Federal Reserve will start tapering off its massive bond-buying programme, known as quantitative easing, and which is credited with helping push borrowing rates lower worldwide.

“The rise in yields has been driven primarily by an improvement in the outlook for the US economy and associated expectations that the Federal Reserve will soon taper the size of its asset purchases,” said Jonathan Lyons, chief European Economist at Capital Economics.

The Fed is currently holding two days of policy talks and investors are anxious to see what Bernanke will say Wednesday at his traditional post-meeting press conference.

Portugal’s 78 billion euro ($105 billion) EU-IMF bailout programme launched in 2011, is intended to bring Lisbon fully back to the bond markets by July 2014.

For now, Portugal, much like fellow bailout recipients Greece and Ireland, only goes to the markets to raise money in the short term.

As part of the bailout, Portugal has agreed to carry out austerity measures including the latest wave of voluntary departures of 30,000 civil servants and the prolonging of the work week to 40 hours from 35.