Iranians reported Saturday that the state broadcaster had muted stadium noise during the previous evening's football match in Tehran, in an apparent attempt to drown out anti-government chants.
Mobile phone footage shared widely on social media showed thousands of fans in Tehran's Azadi stadium chanting "Death to the dictator" during the fixture between the capital's Esteghlal and Tractor Sazi from the northwestern city of Tabriz.
Although the video could not be independently verified, it coincided with a decision by state broadcaster IRIB to mute the sound and avoid shots of the crowd.
"Yesterday, when the football was being shown, the sound in the stadium was turned down to such a level that one would think they were playing in an alleyway," said one Twitter user.
IRIB's football commentators blamed "network disruption" for the low volume, without giving details.
"They turned down the volume so no one could hear the slogans," said another Twitter user.
Iran has seen nationwide strikes and protests in recent weeks, focused on high prices and unemployment but also featuring radical political slogans.
The authorities have acknowledged anger over the economic situation -- which has been exacerbated by the United States' reimposition of sanctions on Tuesday following its abandonment of a landmark 2015 nuclear deal.
But they say any political agitation is the work of outside instigators, fomented by the US, Saudi Arabia and Israel.
Heavy reporting restrictions and reports of mobile internet black-outs in affected areas have made it difficult to verify claims by the authorities and on social media.