GENEVA, Oct 15 (Reuters) - Turkey could be "deemed responsible" for summary executions by an affiliated armed group of several Kurdish fighters and a politician, reportedly shown on videos on social media at the weekend, the United Nations human rights office said on Tuesday.

U.N. human rights spokesman Rupert Colville told a briefing in Geneva that it was obtaining footage of the killings, apparently carried out by Ahrar al-Sharqiya fighters near Manbij.

"Turkey could be deemed as a state responsible for violations by their affiliated groups as long as Turkey exercises effective control of these groups or the operations in the course of which those violations occurred," Colville said. "We urge Turkish authorities immediately to launch an impartial, transparent and independent investigation." (Reporting by Stephanie Nebehay; Editing by Alex Richardson)