Iran said it was reviewing the latest US proposal that sources say would end the fighting but leave several key issues open, as US President Donald Trump claimed a deal was very possible but also warned of renewed fighting if Tehran rejected the deal.

Irans state-run ISNA news agency cited a Foreign Ministry spokesman as saying Tehran had received the US proposal and was studying the details, even as he suggested there were provisions that were unacceptable to leaders of the Islamic republic.

The US proposal to end the war is still "under review," Esmaeil Baqaei was quoted a saying, adding that Tehran will convey its response to mediator Pakistan after "finalizing its opinion."

Still, Trump said Pakistani-mediated talks were progressing well.

"They want to make a deal. We've had very good talks over the last 24 hours, and it's very possible that we'll make a deal," Trump told reporters in the Oval Office on May 6.

Those remarks voiced a more optimistic note following a social media posting earlier in the day in which in which Trump threatened to restart the US bombing campaign against Iran and labeled the possibility of Tehran agreeing to the US proposal a "big assumption."

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The two sides remain at odds over a variety of issues, including Iran's ability to enrich uranium and its control of the Strait of Hormuz, the crucial waterway through which some 20 percent of the world's oil and gas supply transited prior to the war, which broke out on February 28.

One-Page Memorandum

Reuters cited a Pakistani source and another person briefed on the mediation as saying an agreement was close on a one-page memorandum that would formally end the conflict.

Discussions would follow on unblocking shipping through the strait, the lifting of crippling US sanctions on Tehran, and on setting limits on Iran's nuclear program, the Reuters sources said.

Tehran has always insisted that its nuclear program is strictly for civilian purposes, while the US, Israel, and others in the West have accused it of attempting to develop a nuclear bomb.

Iran's semiofficial Tasnim news agency, citing an unnamed source, said the US proposal contained some unacceptable provisions, although it did not specify which ones.

Iranian lawmaker Ebrahim Rezaei, who also serves a spokesman for the Iranian parliament's foreign policy and national security committee, called a previous text of a US proposal "more of an American wish-list than a reality."