Finland's outgoing prime minister Jyrki Katainen is to become the EU's interim Economics Affairs commissioner.

He will replace compatriot Olli Rehn who is leaving to join the European Parliament, the EU said today. 

"I decided to attribute to Jyrki Katainen all the responsibilities so far performed by Olli Rehn," said European Commission chief Jose Manuel Barroso on announcing Rehn's successor to the top EU economic job. 

Katainen, 42, announced in April that he would resign to pursue a career in Brussels.

He has made no secret of his intentions to be considered a compromise candidate to head the Commission should member states reject the controversial appointment of former Luxembourg leader Jean-Claude Juncker. 

The conservative Katainen takes the economics portfolio until October 31, when new leadership is set to take over the Commission, the EU's executive body staffed by 28 people, one for each member state. 

Katainen takes the job amid a push by centre-left leaders to ease the Commission's strict budget rules that are blamed by some for the sluggish growth and high unemployment still gripping Europe. 

Barroso said no government had actually requested to modify the rules, known as the Stability and Growth Pact, adding that he believed the Commission was unfairly singled out for imposing economic hardship on member states. 

"Certain people are unfairly trying to make it seem that someone in Brussels is imposing their views," he said.

Katainen will be replaced as Finnish prime minister by the 46-year-old Alexander Stubb, who was elected by the ruling conservative party on Saturday to form a new government.