Former US officials called Monday for President Barack Obama to pursue diplomacy with Iran's new president after Israel showed a hard line over Tehran's nuclear program.

In their latest letter to Obama, the ex-policymakers said the election of centrist cleric Hassan Rowhani, who will assume the presidency on August 3, "presents a major potential opportunity."

"We strongly encourage your administration to seize the moment to pursue new multilateral and bilateral negotiations with Iran once Rowhani takes office and to avoid any provocative action that could narrow the window of opportunity for a more moderate policy out of Tehran," they wrote.

The letter called on the United States to prepare to "leverage" its sanctions, which have pummeled the Iranian economy, in exchange for concessions.

The letter's 29 signatories included retired veteran diplomat Thomas Pickering, who served as US ambassador to the United Nations; Anne-Marie Slaughter, who was a top aide to former secretary of state Hillary Clinton; and Larry Wilkerson, the chief of staff to former secretary of state Colin Powell.

The letter comes a day after Prime Minister Benjamin Netanyahu warned that Israel will "have to address this question of how to stop Iran, perhaps before the United States does."

Netanyahu, who has seized on outgoing Iranian president Mahmoud Ahmadinejad's strident remarks on Israel and the Holocaust, called Rowhani "a wolf in sheep's clothing."

Netanyahu said that Rowhani, who has called for a better relationship with the West, wanted to "smile and build a bomb."

Netanyahu's remarks to CBS News come as US Secretary of State John Kerry conducts exhaustive diplomacy to try to restart talks between Israel's right-leaning government and the Palestinians.

Last week, two members of the House of Representatives -- Republican Charles Dent and Democrat David Price -- also called for Obama to "utilize all diplomatic tools" with Iran's new president.

The lawmakers noted that Iran's president had limited powers but said it "would be a mistake not to test" Rowhani.

"We must also be careful not to preempt this potential opportunity by engaging in actions that delegitimize the newly elected president and weaken his standing relative to hardliners within the regime who are opposed to his professed 'policy of reconciliation and peace,'" they wrote in a letter.

US, European, Russian and Chinese officials meet Tuesday in Brussels to discuss the next steps on Iran.

Obama at the start of his presidency offered talks with Iran, which has not had relations with the United States since the 1979 Islamic revolution overthrew the pro-Western shah.

But the United States later led a drive to cut off Iran's oil exports, its key export, as a way to pressure the regime over its controverial nuclear work.