Brussels (CNN) European Commission President Jean-Claude Juncker has lashed out at "stupid nationalists" on the eve of European elections in which euroskeptic politicians are expected to make gains in the European Parliament.

In an interview with CNN on Wednesday, the outgoing president said he was only too aware of the threat that nationalist politicians pose to European solidarity, which Juncker called the "main objective of the EU."

Some polls project that populists may become the most powerful group in the parliament following this week's elections in all 28 EU nations, resulting in a lasting impact on the future of the bloc and the continent at large. "These populist, nationalists, stupid nationalists, they are in love with their own countries," Juncker told CNN in his Brussels office.

"They don't like those coming from far away, I like those coming from far away ... we have to act in solidarity with those who are in a worse situation than we are in," he said.

When asked why he thought that anti-EU forces were more successful in mobilizing their base than pro-Europeans, Juncker replied: "It's always easier to mobilize negative forces than to mobilize positive forces."

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