Stance undermines Russian claim on Sunday that Israeli president had taken attack option off menu.
Israel is keeping its options open to deal with the Iranian nuclear programme, a senior official said on Monday, after the Russian president said he had been assured it would not take military action.
Russian President Dmitry Medvedev made the comments in an interview with US television, excerpts of which were released by the Kremlin on Sunday.
"When Israeli President (Shimon) Peres was visiting me in Sochi recently, he said something very important for all of us: 'Israel does not plan any strikes on Iran, we are a peaceful country and we will not do this'," Medvedev said.
Peres's office declined to comment on the remarks on Monday.
But Deputy Foreign Minister Danny Ayalon reiterated what Israeli leaders have said repeatedly - that the Jewish state is keeping all options open when it comes to its arch-foe.
"All options remain on the table," Ayalon was quoted as saying by his spokesman. "It is certainly not a guarantee."
Ayalon later told Israel's army radio that Medvedev could have misunderstood what Peres said, or that his words may have been wrongly interpreted.
"Notwithstanding our respect for the Russian president, he is not in a position to speak in the name of Israel. There has been no change in our position."
Israeli chief of staff Gabi Ashkenazi joined in the debate, saying a nuclear Iran would be a threat to the Middle East and "the entire free world" as well as the Jewish state.
"We all understand that the best way of coping is through international sanctions," he told army radio. "I hope that Iran will understand this.
"I think that if not, Israel has the right to defend itself, and all options are open. The IDF's (Israel Defence Forces) working premise is that we have to be prepared for that possibility, and that is exactly what we are doing."
Widely considered to be the Middle East's sole if undeclared nuclear power, Israel, like the West, suspects Iran of trying to develop atomic weapons under the guise of its nuclear programme, a charge Tehran denies.
Israel considers the Islamic republic its top enemy after repeated statements by President Mahmoud Ahmadinejad that it is doomed to be "wiped off the map" and that the Holocaust was a "myth."