LOS ANGELES - Israeli Prime Minister Ehud Olmert called on Tuesday for moderate Arab countries to unite against Iran and said the world must not wait any longer to thwart its nuclear ambitions.

Israeli Prime Minister Ehud Olmert acknowledges the crowd before addressing the United Jewish Communities 2006 General Assembly at the Los Angeles Convention Center in Los Angeles, California November 14, 2006. [Reuters]

"We have reached the pivotal moment of truth regarding Iran," Olmert said in an address to American Jewish groups.

"If Iran achieves the ability to produce nuclear weapons, as we know it is seeking to do, we will enter a new era of instability unlike any the world has ever seen," he said. "We cannot afford to wait."

He said Israel "cannot tolerate those who challenge" its right to exist while actively seeking to develop "catastrophic weapons." But the Israeli leader stopped short of warning of any military moves against the Islamic Republic.

Olmert made the comments to the General Assembly of the United Jewish Communities of North America a day after White House talks with President George W. Bush in which both men took a tough line against Iran's nuclear program.

"A coalition of moderate Arab countries can and must unite their common interest in preventing Iran from undermining stability in the Middle East," he said, without naming those states.

"This coalition must struggle against the dangers of radical Islam that manipulate the very source of Islam itself."

Olmert praised Bush for taking the lead in "preventing Iran's nuclearization" and said he spoke with the president on the issue at length.

"His determination to prevent this most serious of developments in unquestionable. But America must have the support of the international community if we are to successfully defuse this mortal threat," Olmert said.

Iran, whose president has threatened to wipe Israel off the map, says it is enriching uranium to generate electricity.

Israel, believed to be the Middle East's only nuclear power, has said repeatedly it wants to take a back seat to US efforts to prevent Iran from building nuclear weapons.