Vice Premier Moshe Ya'alon said on Friday he feared Iran did not believe it faced a real military threat from the outside world because of mixed messages from foreign powers, including the United States.

"We have an exchange of views, including with our friends in the United States, who in our opinion, are in part responsible for this feeling in Iran," he told Israel's 100FM radio station.

"There are many cracks in the ring closing tighter on Iran. We criticize this," he said, also singling out UN Secretary General Ban Ki-moon for traveling to Tehran this week.

Ya'alon's statements came a day after Chairman of the US Joint Chiefs Martin Dempsey said that he did not want to be "complicit" if Israel chose to strike Iran's nuclear program, positing that a premature attack would dissolve the international pressure on the Islamic Republic.

Speaking to journalists in London, Dempsey said an attack would "clearly delay but probably not destroy Iran's nuclear program," but added that the "international coalition" pressuring Iran "could be undone if it was attacked prematurely".

"I don't want to be complicit if they [Israel] choose to do it," he added.

Dempsey's comments followed a White House statement that Iran had a limited window of time to stop its atomic work and diplomatic terms offered by the Western world will not remain open "indefinitely."

Prime Minister Binyamin Netanyahu has said he will speak out about the dangers of Iran in an address next month to the UN General Assembly in New York.

He is also expected to hold talks with US President Barack Obama during his visit. A senior Israeli official told Reuters this month that Netanyahu would be looking for a firm pledge of US military action if Iran does not back down.