WASHINGTON (AP) — A flurry of diplomatic contacts and reports of major progress suggest that indirect talks between the U.S. and Iran may be nearing an agreement. That's despite efforts by U.S. officials to play down chances of an imminent deal that would bring Washington and Tehran back into compliance with the 2015 nuclear deal.

With the negotiations in Vienna on hiatus, the U.S. and Britain denied Iranian reports that any agreement was at hand with Iran for a swap of American and British prisoners. Such an exchange could be a confidence-building measure to revive the nuclear deal.

A U.S. return to the deal would be the biggest and most controversial foreign policy initiative in the early months of Joe Biden's presidency. It would revive a deal that top Biden aides put together during their years in the Obama administration, only to see President Donald Trump pull out and try to prevent the U.S. from ever returning. Rejoining it — and making the concessions required to do so — would enrage Republicans and likely unsettle Israel and Gulf Arab allies.

Even as Secretary of State Antony Blinken and British Foreign Secretary Dominic Raab rejected the prisoner swap reports at a news conference Monday in London, senior American diplomats were in the Middle East meeting Gulf Arab leaders. And two of the nuclear deal's biggest proponents in Congress — Democratic Sens. Chris Coons and Chris Murphy — were touring the region.

Those discussions follow a week of top-level meetings in Washington between Biden; his national security adviser, Jake Sullivan; Blinken; his deputy, Wendy Sherman; special Iran envoy Rob Malley; and others with the head of Israel's spy agency and Israeli Prime Minister Benjamin Netanyahu's top national security aide.

The Israelis are adamantly opposed to any U.S. rapprochement with Iran, which they regard as an existential threat to the Jewish state. At least three separate meetings were held with the Israelis last week, including one Friday with Mossad chief Yossi Cohen at which Biden made an appearance. White House press secretary Jen Psaki said Cohen was briefed on the Vienna discussions "and the progress being made there."

Later Friday, and on Saturday, reports emerged from Iran and Iran-linked media outlets that an agreement had been struck on what the U.S. would provide in return for Iran returning to compliance with the 2015 deal, which had given billions of dollars in sanctions relief in exchange for curbs on its nuclear program. On Sunday reports of the prisoner swap deal emerged.

U.S. officials were quick to bat those reports down as premature and inaccurate, although the broad contours of potential sanctions relief are well-known and Washington has made no secret of its eagerness to free Americans held in Iran.

Administration officials have allowed that limited progress has been made at the talks in Vienna, where Malley is heading the U.S. delegation. Malley was a key figure in the Obama administration's negotiation of the original nuclear deal in 2015, as were Sherman and Sullivan, who respectively led those talks and took part in secret meetings that paved the way for the agreement.

The Biden administration reacted sharply to the Iranian reports. The State Department said "we are not at the cusp of any breakthrough" and dismissed the prisoner swap claim as false. "Unfortunately, that report is untrue," White House chief of staff Ron Klain said Sunday.

Sullivan himself has been cautious in public comments about the talks, stressing that things stand at a "unclear place in Vienna." At a virtual meeting of the Aspen Security Forum on Friday, he underscored that the talks were a "real negotiation" while acknowledging the indirect nature of the discussions have made the undertaking somewhat "inefficient."

"I guess good faith is always in the eye of the beholder and we believe the Iranians have come in a serious way to have serious discussions about details and the teams are working through those details now," he said.

Thus, the surge in diplomatic activity as negotiators prepare for a fourth round of talks in Vienna has given supporters of the deal that Trump withdrew from in 2018 reason for hope. And it has caused deal opponents great angst.

Complicating any potential resolution either in the short- or medium-term is the significant array of opponents lined up to try to frustrate a deal. In addition to the Gulf Arabs and Israel, there is strong opposition from Republican members of Congress who are already trying to pass legislation to block it. In Iran, elements of the hard-line Islamic Revolutionary Guard Corps appear to be using the Vienna talks to thwart a candidacy of Foreign Minister Mohamed Javad Zarif in presidential elections this year.

Deal critics have taken issue with the negotiating tactics of Malley and his colleagues, alleging that they are giving away the leverage on Iran that Trump created when he pulled out of the deal and imposed sweeping new sanctions. In fact, any U.S. return to the deal would require the easing of many of those sanctions, including possibly ones that were imposed for non-nuclear reasons, such as terrorism, ballistic missile activity and human rights abuses.

Deal supporters, on the other hand, have lashed out at that criticism, accusing the other side of rejecting diplomacy and cheerleading for war. They argue that sanctions relief is the only way to bring Iran back into compliance with the agreement and shut down its pathways to a nuclear weapon.

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Associated Press writer Aamer Madhani in Chicago contributed to this report.