Investigators questioned Sergei Udaltsov, 35, the shaven-headed activist known for his punchy rhetoric and radical politics, after a pro-Kremlin national channel alleged in a documentary that he was plotting a violent uprising. Udaltsov has dismissed the film aired October 5 as the "delirium of a lunatic". 

Investigators announced this evening that Udaltsov would not be detained on the charge of preparing mass riots but would need to sign a written undertaking not to travel, as he remained inside their Moscow headquarters.