The BBC's Persian TV service is being jammed from within Iran due to its coverage of the unrest in Egypt.
It appears that the trigger point was a joint broadcast on Wednesday by the corporation's Persian and Arabic services in which Iranian and Egyptian callers exchanged views.
Many Iranian viewers said during the interactive programme that they were watching events unfold in Cairo extremely closely.
Peter Horrocks, head of BBC Global News, called for an end to the jamming, saying: "It is wrong that our significant Iranian audience is being denied impartial news and information...
"The BBC will not stop covering Egypt and it will continue to broadcast to the Iranian people."
BBC Persian TV launched in 2009 and has suffered similar attempts to interfere with its signal intermittently ever since. But it continues to stream live online.
Coincidentally, today marks the 31st anniversary of the uprising by the Iranian people against the Shah.
Source: BBC Global News press release
