MOSCOW — Men in Cossack fatigues attacked a group of anti-Kremlin activists led by the anti-corruption crusader Aleksei A. Navalny in southern Russia on Tuesday, in a melee that was captured on video and quickly uploaded to Facebook.

Mr. Navalny and his associates were returning to Moscow from a hiking trip in southern Russia when a group of men threw bags of milk at them in the entryway to an airport in the Black Sea resort of Anapa.

A brawl ensued, with the attackers punching opposition activists and throwing some of them to the ground. Wearing signature Cossack black-and-red fleece hats, the attackers yelled “occupiers” and “get off our land.”

Afterward, one of the Cossacks argued on the Govorit Moskva radio station that, the shower of milk notwithstanding, a member of Mr. Navalny’s group had started the fight. A review of the video of the confrontation does seem to back up the claim, with an activist in a red shirt throwing an elbow at an older man.