The BBC has said that Iran is behind a "sophisticated cyber-attack" aimed at disrupting the BBC Persian Service.
Beeb director general Mark Thompson is set to give a speech at the Royal Television Society in which he will describe a coordinated attack on the internet service and two satellite feeds into Iran.
"We regard the coincidence of these different attacks as self-evidently suspicious," Thompson will say according to a BBC News report.
The public broadcaster chief will not go into further detail on the attacks but will reiterate that the beeb is "taking every step we can, as we always do, to ensure that this vital service continues to reach the people who need it."
It's thought that the internet site of the attack was a general denial of service attack that saw some parts of the BBC unable to access the internet including email.
Lobby group Reporters Without Borders released a report entitled "Enemies of the Internet" earlier in the week in which the group said that Iran's internet access restrictions meant that the Iranian web bore no resemblance to the open web.
Iran can now also block the internet TCP ports used by VPN clients to bypass the censorship firewall.
Thompson blogged last month, describing the "relentless pressure" the Iranian regime was placing on BBC Persian Service journalists including targeting family members of BBC staff still residing in Iran.
"The BBC calls on the Iranian government to repudiate the actions of its officials," Thompson said at the time.