President Hassan Rouhani yesterday defended a nuclear deal criticized by Iran's conservatives after top Republicans vowed to do their utmost to scrap President Barack Obama's signature foreign policy move with Iran.

The elite Revolutionary Guards, a powerful political, economic and military force, have started sniping at the deal, saying it endangers Iran's security, and have also hit out at a UN Security Council resolution passed on Monday endorsing it.

Under the July 14 accord, sanctions will be gradually removed in return for Iran accepting long-term curbs on a nuclear program that the West has suspected was aimed at creating a nuclear bomb. Iran denies it seeks a nuclear bomb.

Rouhani argued that the deal reflected Iranians' wishes. Pinning his political prestige to the agreement, he suggested that blocking the deal would ignore what Iranians had sought when they elected him to office in 2013.

"This is a new page in history," he told a medical conference broadcast live on television. "It didn't happen when we reached the deal in Vienna on July 14, it happened on 4th of August 2013 when the Iranians elected me as their president."

Many analysts see the chance of the Iranian leadership eventually rejecting the deal as small, since Tehran needs the lifting of sanctions to help its isolated economy.

Political analysts say the guarded welcome given the agreement by Supreme Leader Ayatollah Ali Khamenei may be intended to absolve him of blame if the accord, which will last for years, falls apart in future.

In US, top Republicans vowed Wednesday to do their utmost to scrap the deal as the biggest pro-Israel lobby prepared for an all-out campaign to pressure wary lawmakers into rejecting the agreement.

A bigger push against last week's historic accord in Vienna was being met with a counteroffensive by senior Obama administration officials, who have already spent hours on in-person and telephone briefings with members of Congress.

As Congress opened a 60-day review of the deal, Republican US House of Representatives Speaker John Boehner told reporters: "Because a bad deal threatens the security of the American people, we're going to do everything possible to stop it."

Obama insists that the Iran deal is the only alternative to more war in the Middle East.

Israel pressed lawmakers on Wednesday to block the deal, with Israeli Ambassador Ron Dermer meeting privately with a group of about 40 House conservatives.

The most influential pro-Israel group, the American Israel Public Affairs Committee (AIPAC), will deploy about 300 lobbyists on Capitol Hill next week to try to convince lawmakers, especially undecided Democrats, to vote against the deal, according to officials in the pro-Israel camp.

Along with AIPAC, other lobbying groups are expected to spend upwards of $20 million, one source said.