The Iranian government has acknowledged that the US is genuinely willing to reach a comprehensive agreement with Tehran, in an unusual assessment of the progress of the ongoing nuclear talks.

It comes after Barack Obama threatened to veto any new sanctions bill that the congress may impose on Tehran, and as Iran’s foreign minister, Mohammad Javad Zarif, was strongly criticised at home for taking a stroll with his American counterpart.

The Iranian government’s spokesman, Mohammad Bagher Nobakht, who is a close ally of the country’s president, Hassan Rouhani, told reporters on Wednesday that Tehran viewed the US administration as determined to end the nuclear standoff with Iran.

“We are seeking the Iranian people’s rights in the nuclear negotiations and our assessment show that they, especially the Americans, have the will to reach an agreement with Iran,” he said, according to the semi-official Fars news agency.

Nobakht’s comments were rare remarks reflecting Tehran’s view of where the other side stands in the nuclear talks.

In his State of the Union address on Tuesday, Obama said new sanctions by the US congress will only jeopardise the chance to peacefully end the nuclear stalemate with Tehran through diplomacy.

“Between now and this spring, we have a chance to negotiate a comprehensive agreement that prevents a nuclear-armed Iran, secures America and our allies – including Israel – while avoiding yet another Middle East conflict. There are no guarantees that negotiations will succeed, and I keep all options on the table to prevent a nuclear Iran,” he said.

“But new sanctions passed by this Congress, at this moment in time, will all but guarantee that diplomacy fails – alienating America from its allies, making it harder to maintain sanctions, and ensuring that Iran starts up its nuclear program again. It doesn’t make sense. And that’s why I will veto any new sanctions bill that threatens to undo this progress.”

In the latest round of nuclear talks, Zarif, who is also Iran’s lead nuclear negotiator, met the US secretary of state, John Kerry, for several hours in Geneva last week. On the sidelines of those talks, Zarif and Kerry took a stroll in the city, which marked rare scenes of the two top officials from the old adversaries having a break together outside negotiations behind closed doors.

In Tehran, pictures of Zarif and Kerry walking in downtown Geneva prompted criticism from the hardline camp, with Mohammad Reza Naqdi, the commander of Iran’s informal voluntary Basij militia, who is a close confidant of the Iranian supreme leader, Ayatollah Ali Khamenei, attacking the Iranian foreign minister for that stroll.

“Apparently, Mr Zarif doesn’t know what kind of a nation he is representing,” Naqdi was quoted as saying by the Dana news agency. “He must apologise to the Iranian people for his inappropriate actions.”

Nobakht was questioned on Wednesday about the controversies surrounding the stroll. The Isna news agency quoted him as responding: “It is silly to say that our diplomacy is weak because these two officials took a stroll.” This sort of criticism was not supported by Iranian people, he said.