Israeli Prime Minister Benjamin Netanyahu said he was ready to order a strike on Iran's nuclear facilities "if necessary", in an interview aired by Channel Two television on Monday.
"I am, of course, ready to press the button if necessary," Netanyahu said in the interview.
"I hope that that will not be the case. In the final reckoning, the responsibility rests with the prime minister and as long as I am prime minister, Iran will not have the atomic bomb," he said.
"If there's no other way, Israel is ready to act."
The Israeli premier's comments came on the eve of the US presidential election and after repeated and unsuccessful pressure from his government on US President Barack Obama's administration to set a clear "red line" for military action against Iran.
They also came after Channel Two reported on Sunday that Netanyahu and defence minister Ehud Barak had given orders in 2010 for the army to prepare an attack against Iranian nuclear facilities.
The orders were later rescinded in the face of the opposition of then chief of staff Lieutenant General Gabi Ashkenazi and then Mossad spy chief Meir Dagan, the television said.
Israel, like its US ally, has consistently refused to rule out a resort to military action to prevent Iran developing the capability to build a nuclear weapon.
Iran denies any such ambition, insisting its nuclear programme is for peaceful power generation and medical purposes only.
The UN Security Council's five permanent members and Germany are involved in negotiations with Iran but several rounds of talks have failed to to produce much progress on increasing the transparency of Tehran's nuclear programme.
Netanyahu insisted Israel was "not rushing into war".
"If we can solve this issue with international pressure, that's even better... But we are serious. This is not a show," the hawkish prime minister said.
Israel, which has the Middle East's sole if undeclared nuclear arsenal, says it regards a nuclear Iran as a threat to its existence.
Ehud Barak has said he doubts negotiations could resolve the Iranian nuclear crisis and predicted that Israel would probably face a decision over whether to strike in 2013.