US President Barack Obama disappointed legislative leaders when he refused to retract his remark that Iranian hard-liners who chant "death to America" are making common cause with the Republican caucus.

White House Press Secretary Josh Earnest said Obama had no intention of taking back his comments that offended several Republican lawmakers, who vowed to derail the Iran nuclear deal when Congress reviews the controversial pact next month.

"The President was pointing out a simple fact," Earnest said, explaining the coalition with Western powers would fall apart if Congress succeeds in killing the deal. "Iran would go back to doing what they did before."

In a daily briefing on Thursday, Earnest pointed out that lawmakers advocating to kill the Iran nuclear deal would leave military action as the only remaining option, saying: "The suggestion that there is a better deal is a fantasy."

Obama delivered the controversial speech at the American University in Washington on Wednesday.

Responding quickly, Senate Majority Leader Mitch McConnell urged Obama to treat the discussion on the Iran nuclear deal with "reverence and respect" by retracting his statement.

In another press conference in the US Capitol, McConnell criticised Obama for treating the issue like a talking point for a political campaign when the president said, "The choice we face is ultimately between diplomacy or some form of war."

Maryland Rep. Steny Hoyer said Obama is using a counterproductive tone in his bid to rally support for the accord ahead of the 60-day review, which Congress is set to undertake on Sept. 8.

"Characterising people who may be in opposition to the agreement as wanting to go to war as an alternative, I'm not comfortable with that, and I wish the White House wouldn't do that," Hoyer said.

Hoyer, the second-ranking Democrat in the House, said there are other alternatives to going to war.

Illinois Rep. Peter Roskam, for his part, dismissed Obama's declaration assuring that rigorous inspections can foil any attempt by Iran to cheat on nuclear proliferation pact.

"The [United States] completely missed ... that the Iranians were building, that they were putting their [nuclear] infrastructure together in the first place," Roskam told Newsmax Now host John Bachman.

"The whole world missed it, frankly, so the declarative statement by Barack Obama that says, 'hey, don't worry, we've got this covered, all is well' is a false claim," the Republican lawmaker said.

He argued that "there's no capacity" to get the 24/7 type of inspection of the Iranian regime based on the deal negotiated by the Obama administration.

A Fox News report said that the White House is already preparing for the likelihood that lawmakers will vote against the deal.

The news channel claimed that the Obama administration is now focusing its lobbying efforts on getting enough Democrats—146 in the House and 34 in the Senate—to sustain a presidential veto that would keep the deal in place.

Only one chamber of Congress is needed to sustain a veto and keep the deal in place.

The White House recently expressed its confidence it can sustain a veto in the House with 16 House Democrats and 11 senators declaring their support for the deal in public.