France's foreign minister is calling for an investigation into the killing of Russian opposition politician Boris Nemtsov, calling it an "assassination that was revolting."

Laurent Fabius said on BFM television Monday that the shooting of Nemtsov in Moscow on Friday night "raises a series of questions." He insisted on a thorough investigation, but would not comment on whether he thought Russian authorities' efforts would be sufficient.

Russian investigators have said they are looking into several possible motives for the killing. The opposition sees the Kremlin as responsible, while Vladimir Putin's spokesman called it a "provocation," possibly to discredit Russia's leadership.

Noting killings of other Russian opposition figures in the past, Fabius said, "The fact is that it is not good to be an opposition figure in Russia."