A US envoy has said Hamas proposed a five-to-10-year ceasefire and a full prisoner exchange during backroom talks that have provoked angry responses from the administration of Benjamin Netanyahu and his conservative backers in Israel and the US.

Adam Boehler, the US special presidential envoy for hostage affairs, told Kan News, an Israeli public broadcaster, that he “does believe” Hamas would eventually lay down its weapons and leave power in Gaza. While he said the series of interviews was meant to explain the US position, he also defended the talks by saying that Washington is “not an agent of Israel”.

“We weren’t prepared to just sit back for two weeks,” Boehler said, adding: “You’ve got a real chance for some movement and seeing hostages home in the next few weeks.”

Those remarks are said to have provoked behind-the-scenes fury from Netanyahu’s strategic affairs adviser Ron Dermer, as well as public anger from rightwingers in the government including the ultranationalist finance minister Bezalel Smotrich.

“[Boehler] attempted to negotiate the release of American hostages. We made it clear to him that he cannot speak on our behalf, and if he wishes to negotiate on behalf of the United States, then good luck to him,” Smotrich told Israel’s Army Radio, according to the Times of Israel.

The Israeli minister did not specify how this message was conveyed to Boehler. However, on Monday, the US secretary of state, Marco Rubio, further sought to tamp down concerns over the talks between Boehler and Hamas.

“That was a one-off situation in which our special envoy for hostages, whose job it is to get people released, had an opportunity to talk directly to someone who has control over these people and was given permission and encouraged to do so. He did so,” Rubio told reporters while flying to Saudi Arabia.

“As of now, it hasn’t borne fruit. Doesn’t mean he was wrong to try, but our primary vehicle for negotiations on this front will continue to be Mr Witkoff and the work he’s doing through Qatar,” Rubio added, referring to Trump’s envoy to the Middle East, Steve Witkoff.

In Israel, the revelation of direct talks between the US and Hamas has provoked mixed emotions. Official reaction from the Israeli government has been limited to a single terse statement by the office of Netanyahu acknowledging the negotiations and some broadly neutral comments from more junior officials.

One key question has been whether Israel knew of the contacts before they were revealed by US-based media. Boehler did not answer questions about when the contacts began during interviews with Israeli media.

Kan, the national public radio network, reported “behind-the-scenes tension between Israel and the US over the direct talks between Trump’s envoy Adam Boehler and the terrorist Khalil al-Hayya, talks that Israel only learned about from sources and only later was formally notified”.

Others have welcomed the prospect of progress towards a diplomatic agreement that might ensure the return of more hostages.

The mass-market newspaper Yedioth Ahronoth said: “Israel was stunned to discover that, behind its back, Trump’s envoy had flirted for weeks in Doha” with Hayya, a senior Hamas official.

“Hamas got what it could only have dreamt of getting under Biden: legitimacy,” the paper wrote.

The newspaper gave details of what it said was “a fraught conversation” between Boehler and Dermer, a close adviser of Netanyahu.

“Dermer thought that the Americans had agreed to an excessively large release of terrorists and that this would set the tone for the talks on the second stage. Boehler was stunned by Dermer’s insolence and spoke about that in conversations with other people,” the newspaper said.

Hugh Lovatt, a senior policy fellow at the European Council on Foreign Relations, described the contacts as “quite a big deal”.

“Let’s see how it plays out. This kind of contact … can be positive. It can certainly move forward diplomacy.”

Lovatt said that Hamas was unlikely to be overawed by dealing with the US.

“Hamas negotiators have been quite professional. They’ve been able to make concessions but also to stand their ground. They are quite a robust partner so that will make a difference.”

The Trump administration has sought to shut out its allies in negotiations both with Hamas and in Ukraine, where advisers are seen to be negotiating with Russia directly on a “reset” in relations and have increased pressure on Ukraine’s president, Volodymyr Zelenskyy, by cutting off military aid and intelligence sharing.

Trump’s envoy to Ukraine and Russia, Gen Keith Kellogg, has said the US cut off support in order to get the Ukrainians’ attention, comparing the tactic to hitting a mule in the face with a wooden beam.