The number of those registered as looking for work rose to 819,300 in a workforce that totals 5.48 million people, an increase of 18.9 percent from the same period a year earlier.

Among youths aged 15-24, the unemployment rate rose to 36.2 percent in the three months from January through March, from 35.4 percent in the last quarter of 2011.

Portuguese Finance Minister Vitor Gaspar said last week that a study was underway to determine why the unemployment rate had spiked.

According to European Commission estimates, Portuguese unemployment is likely to rise to 15.5 percent this year before dipping to 15.1 percent in 2013.

The government has issued an official forecast of 14.5 percent for 2012.

Portugal agreed to strict austerity measures in exchange for a rescue package worth 78 billion euros ($99 billion) from the European Union and International Monetary Fund.

The measures have contributed to a recession in Portugal, where international creditors expect economic activity to contract by 3.3 percent this year after shrinking by 1.6 percent in 2011.

The economy did better than expected in the first three months of this year however, contracting by just 0.1 percent on a quarterly basis, the smallest decline since the country entered recession in late 2010.