BBC Director General Mark Thompson said the Internet attack coincided with efforts to jam two of the service's satellite feeds into Iran, BBC News reported Wednesday.
"We regard the coincidence of these different attacks as self-evidently suspicious," he said Wednesday, although he refrained from explicitly accusing Tehran.
Last month, Thompson alleged Iranian authorities had arrested and threatened families of BBC journalists to force them to quit the Persian news service.
"It now looks as if those who seek to disrupt or block BBC Persian may be widening their tactics," he said.
BBC Persian staff provide Farsi-language TV, radio and online services beamed at Iran, where the hard-line Islamic government views foreign media with suspicion.
The BBC's TV service has often been jammed and is only available to owners of illegal satellite receivers, BBC News said.
"We are taking every step we can, as we always do, to ensure that this vital service continues to reach the people who need it," Thompson said.