Despite soothing assurances from Iran's new leaders, Israeli Prime Minister Benjamin Netanyahu implored US President Barack Obama to keep punishing sanctions in place against Tehran - and even tighten them if the Islamic republic advances its nuclear programs while negotiating with the US.
Netanyahu nevertheless signalled he would not block Obama's efforts to seek a diplomatic resolution to the nuclear impasse, even as he expressed scepticism about the Iranian government.
"If diplomacy is to work, those pressures must be kept in place," Netanyahu said of the sanctions during an Oval Office meeting with Obama.
The two men met three days after Obama's historic phone call with Iranian President Hassan Rouhani, which marked the first direct conversation between a US and Iranian leader in more than three decades. While the election of Rouhani, a more moderate-sounding cleric, has been viewed optimistically by the Obama administration, Netanyahu has dismissed the new Iranian leader's outreach as a "smiley campaign" aimed at buying Tehran more time to pursue a bomb.
Obama, who has long called for a negotiated solution to the Iranian nuclear dispute, said it was important to test the possible diplomatic opening.
But he insisted that US officials were "clear-eyed" as they enter talks with the Iranians.
"Our hope is that we can resolve this diplomatically," Obama said. "But as president of the United States, as I've said before and I will repeat, that we take no options off the table, including military options."
The president did not offer Netanyahu any public assurances about the future of the American sanctions, which have resulted in skyrocketing inflation and unemployment in Iran. But he credited the penalties with pushing Rouhani to seek a nuclear deal in exchange for economic relief.
The sudden prospect of a thaw between the US and Iran has threatened to further strain the often-tense ties between Obama and Netanyahu. While the relationship has improved somewhat in recent months, Netanyahu has long been sceptical of Obama's preference for negotiating with Iran and has repeatedly pressed his US counterpart to toughen his threats of military action should Tehran get close to producing a nuclear weapon.
Ahead of his visit to the US, Netanyahu made a series of derisive remarks about Rouhani's efforts to woo Obama and vowed to "tell the truth in the face of the sweet talk and the onslaught of smiles".
But the Israeli leader was publicly more subdued while sitting side-by-side with Obama at the White House. He thanked the US president for his efforts to curb the Iranian nuclear program and for calling on Rouhani to back up his words with actions. And in a possible sign of moderation, Netanyahu repeatedly said Iran must give up its "military" nuclear program, raising the possibility that Israel might be open to tolerating limited nuclear activities by Iran.
In the past, Netanyahu has said that Iran must halt all enrichment of uranium, a process that can have both military and civilian uses.
Iran has offered to open its nuclear facilities to international inspectors as part of broad negotiations with the United States but insists the nuclear program is its right and is for peaceful purposes only. The US, Israel and other allies have long accused Iran of seeking a bomb.
Netanyahu was expected to bring intelligence with him to Washington that Iran was on the cusp of achieving the ability to produce a nuclear weapon. He is also expected to argue that Iran is nearing nuclear weapon capabilities when he addresses the United Nations General Assembly on Tuesday.
Obama and Rouhani both addressed the UN last week. Their overlapping trips to New York, combined with an exchange of letters ahead of their arrival, led to speculation that the two would meet face-to-face. But US officials said the Iranians told them an in-person meeting would be "too complicated".
However, Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif did hold a one-on-one meeting in New York, setting the stage for Friday's phone call between the leaders.
A series of other pressing regional matters, including Syria and Middle East peace efforts, were also on the agenda Monday during the talks between Obama and Netanyahu. The leaders last met in person in March when Obama made his first trip to Israel as president.
Obama's visit helped lay the groundwork for a new round of peace talks between the Israelis and Palestinians. However, the prospect of an elusive breakthrough seems as slim as ever.
The president commended Netanyahu for entering into "good-faith negotiations" with the Palestinian Authority. The Israeli leader said he remains committed to a peace accord. Netanyahu also expressed hope that a breakthrough with the Palestinians could lead to improved Israeli relations with other Arab nations.
On Syria, Obama said a recent international agreement to remove the Assad government's chemical weapons stockpiles was aimed not only at reducing the threat to Syrian civilians but also neighbouring Israel.
The two leaders also discussed the tense political situation in Egypt, the first Arab nation to sign a peace treaty with Israel. Obama said he continues to have concerns about the Egyptian military's ouster of its country's first democratically elected leader. But he said he was committed to maintaining a constructive relationship with Egypt, in part to help uphold its accord with Israel.