Probe into Alexei Navalny's death ongoing: Kremlin

"It's ongoing, all the necessary actions are being carried out," Kremlin spokesman Dmitry Peskov told reporters.

The Kremlin said Monday the investigation into the death of Alexei Navalny was ongoing as it slammed "vulgar statements" over the Kremlin's responsibility for his death.

A portrait of opposition leader Alexei Navalny and flowers are seen during a protest in front of Russian embassy in Belgrade, Serbia. (AP)

"It's ongoing, all the necessary actions are being carried out," Kremlin spokesman Dmitry Peskov told reporters when asked about the investigation, adding that Moscow considered a series of "blatantly vulgar statements" about Navalny's death to be "absolutely unacceptable".