JERUSALEM - Israel's recently retired spy chief says a military strike against Iran's nuclear program would be "stupid," Israeli media reported Sunday.

His remarks challenge Israeli Prime Minister Benjamin Netanyahu's position that Iran won't curb its nuclear ambitions unless it thinks it is threatened with military action.

Israel considers Iran to be its most formidable foe and like the West, does not believe Tehran's claims that it is not developing nuclear weapons.

Former spymaster Meir Dagan told a weekend conference that an effective attack on Iran would be difficult because Iranian nuclear facilities are scattered and mobile, Israeli media reported.

Dagan also cautioned that a strike would be liable to trigger war with Iran and possibly Syria.

This is the first time Dagan has publicly expressed his blunt opposition to a military strike against Iran, though he has expressed reservations privately, media have reported.

There was no immediate comment from the prime minister's office.

But Defense Minister Ehud Barak criticized the comments.

"I'm not sure this stance is correct," he said. "I'm pretty sure that if we are speaking about matters of wisdom ... it is not wise to share such thoughts with the public."

Finance Minister Yuval Steinitz said he was "shocked" by Dagan's comments, calling them "unnecessary."

Israeli officials have said repeatedly that Iran must not be allowed to become a nuclear power and that all options to prevent that must remain on the table. But they have never explicitly said Israel would carry out such a strike.

Israel destroyed an unfinished Iraqi nuclear reactor in a 1981 airstrike, but in that case, destroying that one target was enough to cripple the nuclear program.

Dagan spoke days before Netanyahu is due to meet with US officials in Washington. It is not clear how his remarks will affect the prime minister's international campaign against the Iranian nuclear program.