Portugal's borrowing costs have risen sharply amid fears of a growing political crisis in the country.
Yields on the country's benchmark 10-year bonds moved above 8% in early trading, while the stock market fell more than 6%.
Earlier this week, the resignations of two leading ministers put pressure on Portugal's coalition government.
The European Commission President, Jose Manuel Barroso, said he was following the situation "with concern".
Portugal received a bailout worth more than 78bn euros ($102bn; £67bn) in May 2011, on the condition it implemented austerity measures.