JERUSALEM – Mortified that the world may be warming up to Iran, Israeli Prime Minister Benjamin Netanyahu is taking an unpopular message to the White House and the United Nations this week: Don’t be fooled by Tehran’s new leadership.

Netanyahu contends Iran is using conciliatory gestures as a smoke screen to conceal an unabated march toward a nuclear bomb.

He will deliver those strong words of caution — and fresh intelligence — in an attempt to persuade the U.S. to maintain tough economic sanctions and not allow the Islamic republic to develop a bomb or even move closer to becoming a nuclear threshold state.

With the White House cautiously optimistic about its dialogue with Iran, Monday’s meeting between Netanyahu and President Obama could be tense.

“I will tell the truth in the face of the sweet talk and the onslaught of smiles,” Netanyahu said before boarding his flight to the U.S. on Sunday. “Telling the truth today is vital for the security and peace of the world and, of course, it is vital for the security of the state of Israel.”

Israeli leaders watched with great dismay what they derisively call the “smiley campaign” by Iran’s new president, Hassan Rouhani, last week. Rouhani delivered a conciliatory speech at the United Nations in which he repeated Iran’s official position that it has no intention of building a nuclear weapon and declared his readiness for new negotiations with the West.

Capping off the visit, Rouhani and Obama held a 15-minute phone call as the Iranian leader was traveling to the airport. By the end of the call, the first conversation between the nation’s leaders in 34 years, Obama was suggesting that a breakthrough on the nuclear issue could portend even deeper ties between the U.S. and Iran. U.S. and European diplomats hailed a “very significant shift” in Iran’s attitude and tone.

For Netanyahu, such sentiments are nothing short of a nightmare.

For years, he has warned that Iran is steadily marching toward development of nuclear weapons, an assessment that is widely shared by the West because of Iran’s continued enrichment of uranium and its run-ins with international nuclear inspectors.

The Israeli prime minister contends Rouhani’s outreach is a ploy to ease international sanctions and buy time. Iran says its nuclear program is for peaceful purposes only.

Israel considers a nuclear-armed Iran an unacceptable threat, given repeated Iranian assertions that the Jewish state should not exist.