French Socialist Segolene Royal said Sunday the arrest of her fellow party member IMF chief Dominique Strauss-Kahn on sex charges was "staggering" but stressed that he was innocent until proven guilty.

"It is staggering news, about which everything remains to be verified," Royal told Europe 1 radio.

Royal ran for president in 2007 and is running again for the Socialist nomination for the 2012 vote, as Strauss-Kahn was widely expected to do before news of his arrest.

She stressed that Strauss-Kahn had the right to be presumed innocent.

"Let us wait for justice to do its work and not turn this into a political soap opera," she said.

Bernard Debre, a lawmaker of President Nicolas Sarkozy's UMP party, called the news of the arrest "inacceptable ... very humiliating for our country," but also acknowledged the presumption of innocence.

"Imagine what this could mean for the job he holds at the IMF and for France," he told Europe 1.