The BBC's Persian television service is being jammed from within Iran following coverage of the political unrest in Egypt, the broadcaster said today.
It has been airing extensive rolling news from the country, including many live transmissions, but believes the impact of this coverage has prompted the interruption which began last night.
Many Iranian viewers claimed to have been watching events unfold in Cairo and elsewhere in the region extremely closely, the Corporation said.
It has vowed to continue its broadcasts to Iran and its coverage of the turmoil in Egypt.
Peter Horrocks, director of the BBC World Service, said: "This jamming should stop immediately.
"The events in Egypt are being viewed by the entire world and it is wrong that our significant Iranian audience is being denied impartial news and information from BBC Persian TV.
"This is a regional story that Persian TV have been covering thoroughly and it is clear from our audience feedback that Iranian people want to know what is happening in Egypt.
"The BBC will not stop covering Egypt and it will continue to broadcast to the Iranian people."
Programmes which may have caused concern within Iran are understood to include a broadcast in which the BBC's Persian and Arabic services joined together for an interactive show in which Iranian and Egyptian callers exchanged views.
The heavy electronic jamming is of satellites used by the BBC in the Middle East to broadcast the BBC Persian TV signal to Iran.
Satellite technicians have traced that interference and have confirmed it is coming from the country, the broadcaster confirmed.
BBC Persian television launched in 2009 and has apparently suffered similar "deliberate attempts" to interfere with its signal intermittently ever since.
BBC Persian TV continues to stream live online.