A leading candidate for Germany's Green party says it won't support anyone hoping to head the European Union's executive branch if that candidate seeks the support of the far right.

Populist and far-right parties critical of the EU are expected to make gains in next month's European parliamentary elections, which are being held in all EU nations.

Sven Giegold said Thursday if the Greens' own candidate for the European Commission presidency fails to win sufficient support — which is likely — the party would seek to form "a clear pro-European majority" in the bloc's parliament.

Giegold told reporters in Berlin that "we won't back anyone who allows themselves to be supported by the far right." The comment was directed toward the center-right European People's Party and its leading candidate, Manfred Weber.