A landmark U.S.-Iran agreement that ended a three-month war and opened the door to broader negotiations has sparked alarm among America's Middle East allies and drawn fierce criticism from Republicans in Washington, with opponents arguing the deal strengthens Tehran while falling short of key U.S. and Israeli objectives.

Signed by U.S. President Donald Trump and Iranian President Masoud Pezeshkian at Versailles on the sidelines of the G7 summit, the 14-point interim accord extends a ceasefire by 60 days and launches negotiations on a permanent settlement, including Iran's nuclear programme. Supporters have hailed it as a historic breakthrough, but critics say it grants Iran legitimacy, sanctions relief and renewed regional influence.

"For Washington and Tehran, this is a grand bargain — the deal of the century, with no turning back," said Lebanese commentator Sarkis Naoum. "The probability of success outweighs the risk of failure. Iran cannot endure further economic pain under sanctions, and Trump has no incentive to start a new war."

Israel sees strategic setback

The strongest regional backlash has come from Israel, where analysts view the agreement as a major reversal of goals pursued during the conflict.

Israeli analyst Danny Citrinowicz described the agreement as a strategic "catastrophe", arguing that what began as a joint U.S.-Israeli effort to weaken Iran had ended with Washington effectively recognising and strengthening the Islamic Republic.

"We went to topple the regime with U.S. backing and ended with Washington effectively giving legitimacy and strengthening the same regime we wanted to bring down," said Citrinowicz, a senior Iran researcher at Israel's Institute for National Security Studies.

According to Citrinowicz, the deal fails to address Israel's key concerns, including Iran's missile programme, its network of regional proxies and the dismantling of its nuclear infrastructure. He also argued that Israel's military campaign in Lebanon had been constrained by a ceasefire framework shaped by Tehran's demands.

"The fallout is both political and strategic. The deal undercuts Netanyahu's narrative on Iran and exposes the limits of his leverage with a U.S. president seen as closely aligned with Israel."

Citrinowicz warned that Iran now has greater room to manoeuvre regionally. "Everything is bad," he said bluntly. "And it's only going to get worse."

If implemented successfully, the accord could provide Iran with an end to the war, phased sanctions relief, renewed oil exports and access to reconstruction funding while preserving its political system.

Lebanon and Gulf states fear shifting balance

The agreement has also raised concerns across Lebanon and the Gulf, where governments and political factions fear a new regional order that cements Iran's influence.

For Lebanon, the deal binds all parties to a 60-day ceasefire and folds the country into a broader U.S.-Iran framework, potentially sidelining separate Beirut-Israel negotiations.

Lebanese President Joseph Aoun warned last week that Iran could not negotiate on Lebanon's behalf regarding ceasefire arrangements and Israel's withdrawal from southern Lebanese territory.

However, sources close to Hezbollah said the opposite was true, arguing that direct U.S.-Iran engagement elevated Lebanon's importance and increased pressure on both Hezbollah and Israel to reach a settlement.

An unnamed Iranian official said Israel's position had weakened since the war.

"Israel has been isolated, after this war, both in the region and in the world," the official said.

Another Iranian official argued Tehran had protected its allies during negotiations.

"Iran got what it wanted...We did not abandon our friends, such as Hezbollah, rather, we were even prepared to go to the extent of walking away from the table and returning to war because of them," the official said.

Concern is particularly acute in Gulf states, where Iranian attacks during the conflict shook confidence in longstanding security arrangements. Regional sources say the agreement is prompting a reassessment of dependence on U.S. protection and accelerating a shift toward accommodation with Iran.

Iran expert Alex Vatanka disputed the notion that the accord represented capitulation to Tehran.

"They tried to take Iran down militarily. They couldn't. The alternative would have been catastrophic — a wider war could have devastated the Gulf for decades," said Vatanka, a senior fellow at the Middle East Institute in Washington.

"The real test lies ahead — in implementation of the deal, in the unresolved nuclear negotiations, and in the regional reactions it will provoke," he said. "It's big, but it's not the end of it. It's just the beginning."

Republicans attack Trump over Iran concessions

The agreement has also triggered a rare backlash within Trump's Republican Party as details of the memorandum circulated on Capitol Hill.

Republican Senator Bill Cassidy called the accord "the worst foreign policy blunder in decades," arguing that Iran had emerged stronger despite the conflict.

"Iran’s nuclear ambitions were not curbed, and they have learned that threatening the Strait of Hormuz works and will undoubtedly leverage it in the future," Cassidy wrote on X.

"Now, 13 Americans are dead, families have paid billions at the pump, sanctions will be lifted, and the bombing has stopped. This is the worst foreign policy blunder in decades."

Republican Senator Roger Wicker, chairman of the Senate Armed Services Committee, expressed concern that the agreement could undermine U.S. military gains and criticised any move to lift sanctions in exchange for further negotiations.

Wicker said it would be wrong to force Israel to stand down against Hezbollah and opposed lifting sanctions or unfreezing Iranian assets "in exchange for Iran's mere agreement to negotiate for another 60 days."

Criticism has also come from influential conservative commentators.

"This MOU appears to be, just from the text, a disaster that does not achieve any of the actual signal goals that were set by the administration," conservative commentator Ben Shapiro told Fox News.

Mark Levin, another prominent Trump supporter, criticised the decision not to include Iran's ballistic missile programme in the agreement.

"This man should never be elected dogcatcher," Levin said of Senator Roger Marshall, calling the omission of ballistic missiles from the deal an "outrage."

"To downplay the damage these missiles do (ask the Arab countries what they think about ballistic missiles) and the significance of not including them in any deal is utterly irresponsible," Levin wrote. "Iran is a terrorist regime that has killed our people, how many more times do we need to be reminded of this."

Trump dismissed the criticism, defending the agreement as a necessary step toward stability and pointing to falling oil prices and rising stock markets.

"These fools, who think I haven’t been tough enough on Iran, when the Stock Market Just Hit A RECORD HIGH, and Oil prices are “tumbling” down, are either jealous, bad people, or stupid. MAKE AMERICA GREAT AGAIN!!! President DJT," he wrote on social media.

With Congress demanding more information and negotiations on a final settlement yet to begin, the agreement has already reshaped political calculations in Washington and across the Middle East. Whether it ultimately delivers lasting peace or strengthens Iran's regional standing remains the central question confronting both Trump's allies and America's partners in the region.