Portugal's borrowing costs rose to a seven-month high as political tensions grow over the country's bailout terms.
Yields on 10-year bonds hit an intraday high of 7.9% before easing back, while the Lisbon stock market closed down by 1.6%.
On Friday, the opposition Socialists demanded a renegotiation of Portugal's bailout terms.
Investors fear disagreements over the bailout will weaken Portugal's commitment to economic reform.
Socialist leader Antonio Jose Seguro told parliament: "We have to abandon austerity politics. We have to renegotiate the terms of our adjustment programme. The prime minister has to recognise publicly that his austerity policies have failed."
Divisions over the bailout have already forced Lisbon to request a delay in a review of the bailout by its creditors - initially due to start on Monday - until the end of August or early September.
