Israel is demanding international action against Iran's nuclear program, after a recent U.N. nuclear agency report found “credible” evidence of Iranian efforts to design a nuclear weapon.

Israeli Prime Minister Benjamin Netanyahu told his Cabinet the report proves Iran is “systematically developing nuclear weapons.”

Israel sees a nuclear-armed Iran as a threat, in part due to frequent Iranian calls for Israel's destruction. Israel is widely-believed to be the only Middle East nation with a nuclear arsenal.

U.S. President Barack Obama urged Russian and Chinese leaders to support his efforts to pressure Iran to stop its sensitive nuclear activities. He spoke to the leaders separately on the sidelines of a regional summit Saturday in Honolulu, Hawaii.

U.S. deputy national security adviser Ben Rhodes said all three leaders were united in their opposition to Iran becoming a nuclear-armed nation. The Russian and Chinese presidents gave no details of their discussions with Mr. Obama.

Western powers have warned that Iran faces more sanctions if it fails to address their concerns raised in the U.N. report. Iran rejected the report and insisted its nuclear program is peaceful.

Russia and China have said additional U.N. sanctions on Iran will not resolve the nuclear dispute.

Mr. Obama has tried to increase pressure on Iran through the United Nations and through unilateral U.S. sanctions. His administration has also insisted that “all options” remain on the table, a reference to possible military action. Republicans seeking to challenge him for the presidency next year criticized his strategy in a nationally-televised debate Saturday, with some saying they would take stronger measures to prevent a nuclear-armed Iran that could escalate to going to war.

Former Massachusetts governor Mitt Romney said he would take military action if other measures failed. Romney said that if he is elected president, Iran “will not have a nuclear weapon,” while predicting that Iran will become nuclear-armed if Mr. Obama wins a second term.

Another Republican hopeful, U.S. House of Representatives Intelligence Committee member Michele Bachmann, accused Iran of working with Syria and militant groups such as Hamas to prepare for a “worldwide nuclear war against Israel.”

Business executive and presidential candidate Herman Cain told the debate that the only way to stop Iran from gaining nuclear weapons is through economic sanctions and support for Iranian opposition groups.

However, Republican candidate and House member Ron Paul said going to war against Iran is “not worthwhile.”