Iran on Tuesday scorned as a "laughing matter" comments by Israeli Prime Minister Benjamin Netanyahu that Tehran is moving closer to making a nuclear bomb.
"The claim of the Zionist regime, is a laughing matter," foreign ministry spokesman Ramin Mehmanparast said at his weekly news conference.
He added that the "Zionist regime is a great violator and an illegitimate regime" that had "illegally stockpiled nuclear warheads."
"They threaten to use these nuclear warheads against other countries," he said, adding that Israel was the "biggest obstacle" to the creation of a nuclear-free Middle East.
Netanyahu said on Monday that Iran was now closer to crossing the "red line" after which it would be able to build a nuclear weapon, but had not yet reached that stage.
He also asked for "stronger pressure and harsher sanctions" on Iran to prevent it from crossing the line.
Netanyahu has publicly aired his differences with President Barack Obama who favours diplomacy and international sanctions against Iran to rein in its atomic programme.
He also has criticised Washington for failing to set its own "red lines" that would trigger military action against Iran, whose leaders have repeatedly called for the disappearance of the Jewish state.
The Islamic republic denies Western claims it is seeking atomic weapons and insists it is enriching uranium to 20 percent purity -- a short technical step from the 90 percent needed for a nuclear bomb -- for a medical research reactor.
Mehmanparast asserted that the process of the converting "20 percent enrichment to fuel rods," for the Tehran Research Reactor is "ongoing," and all of the conversion is reported to the International Atomic Energy Agency.
Israel, the Middle East's sole, albeit undeclared, nuclear power, has not ruled out military action against the Islamic state if diplomacy fails to stop its nuclear activity.
Tehran is under a series of international over its nuclear enrichment activities which have created a severe economic crisis, including choking Iran's banking system and limiting oil exports, its main foreign revenue earner.
Iran and the P5+1 group of the United States, China, Russia, Britain, France and Germany are to resume negotiations in Almaty, Kazakhstan on February 26 after an eight-month hiatus, following up three failed meetings last year.
The talks have been going on for around a decade without any tangible results.