UN leader Ban Ki-moon is "dismayed" by the latest anti-Israel comments made by Iranian leaders, a spokesman said.
President Mahmoud Ahmadinejad's attack on Israel as being a "cancerous tumour" has already been condemned by the United States and France. Ahead of mass demonstrations in Tehran on Friday, supreme leader, Ayatollah Ali Khamenei, said that Israel will "disappear".
"The secretary general is dismayed by the remarks threatening Israel's existence attributed over the last two days to the supreme leader and the president of the Islamic Republic of Iran," said a statement released by his spokesman Martin Nesirky.
Ban "condemns these offensive and inflammatory statements," he said.
Ahmadinejad and other Iranian leaders have frequently made such statements to condemn Israel.
The UN secretary general said that "all leaders in the region should use their voices at this time to lower, rather than to escalate, tensions," added the spokesman.
"In accordance with the United Nations Charter, all members must refrain from the threat or use of force against the territorial integrity or political independence of any state."
Iran is locked in a nuclear showdown with the United States and its allies in Europe. Israeli media has speculated that the Israeli military could attack Iran's nuclear facilities.