There was no immediate comment from the prime minister's office.
Diskin's remarks followed a furor over comments made on Wednesday by Israel's serving military chief, Benny Gantz, which starkly contrasted with Netanyahu's rhetoric on Iran. Gantz said he did not believe the Iranian leadership was prepared to "go the extra mile" to acquire nuclear weapons because it was "composed of very rational people" who understood the consequences.
In what was seen as a veiled rebuke to the prime minister, Gantz added: "Decisions can and must be made carefully, out of historic responsibility but without hysteria."
The chief of staff later attempted to gloss over suggestions of a breach between the military and political leaderships, telling reporters there was "really no distance" between his view and the prime minister's.
Neither Netanyahu nor Barak have moderated their rhetoric. The prime minister recently said that those who downplayed the threat from a nuclear Iran "have learned nothing from the Holocaust". He added: "The Iranian regime is openly calling for our destruction and working frantically for the development of nuclear weapons as a means to that end."
On Thursday, Barak said the chances of Iran halting its nuclear program in response to international sanctions appeared low. Iran, he said, was not "rational in the western sense of the word".
Diskin's comments also put him in agreement with the former head of the Mossad, Meir Dagan, who has said that attacking Iran was "the stupidest thing I have ever heard" and that the Iranian regime was rational.
Intellpuke: You can read this article by Guardian Correspondent Harriet Sherwood, reporting from Jerusalem, in context here: www.guardian.co.uk/world/2012/apr/28/israeli-spy-chief-warns-netanyahu-barak