Oman’s foreign minister has claimed the US has “lost control of its own foreign policy” and accused Israel of persuading Donald Trump’s administration to go to war with Iran – a conflict he described as a “catastrophe” and “grave miscalculation”.

Writing in the Economist, Badr Albusaidi, the Omani minister who mediated the latest nuclear talks between Iran and the US, offered an unusually damning assessment of events leading up to the US and Israel’s bombing of Iran and the war that it has triggered across the Middle East.

“It was a shock but not a surprise when on 28 February – just a few hours after the latest and most substantive talks – Israel and America again launched an unlawful military strike against the peace that had briefly appeared really possible,” wrote Albusaidi.

Of all the Gulf countries, Oman was the most vocal and publicly proactive in trying to halt a US attack on Iran, although other states – including the UAE and Qatar – also worked hard to find diplomatic solutions and warned Trump that a war would be devastating for the region.

According to Albusaidi, Iran and the US had been on the “verge of a real deal” in the nuclear negotiations held in Geneva in February, describing the talks as “substantive”.

As revealed by the Guardian this week, a similar assessment had been made by the UK’s national security adviser, Jonathan Powell, who had attended the final stages of the nuclear talks. According to sources, he had been surprised at the significant “progress” towards a permanent, substantive nuclear deal and judged that it was enough to halt a war between the two sides.

The US negotiating team consisted of Trump’s special envoy, the real estate developer Steve Witkoff, and his son-in-law Jared Kushner. They reportedly brought no experts with them.

Sources said the Iranians had agreed to highly significant concessions including a reduction and pause on their enrichment of uranium and also offered the US the chance to participate in a future civil nuclear programme, in exchange for a lifting of sanctions and unfreezing of assets.

A final phase of negotiations had been planned for the following week in Vienna, but 48 hours after the talks finished, the US and Israel began their strikes on Iran.

Albusaidi blamed “Israel’s leadership” for persuading US president Trump to join the war on the false basis that Iran’s regime would offer an “unconditional surrender” after the assassination of its supreme leader, Ayatollah Ali Khamenei.

“The American administration’s greatest miscalculation, of course, was allowing itself to be drawn into this war in the first place,” he wrote. “This is not America’s war, and there is no likely scenario in which both Israel and America will get what they want from it.”

Albusaidi described the war, and its wider impact on the Gulf region which has borne the brunt of Iran’s retaliation, as a “catastrophe”, with neither side showing any willingness to negotiate.

He called for an end to the conflict and a return to bilateral negotiations, arguing that “for Israel to achieve its stated objective will require a long military campaign to which America would have to commit troops on the ground, opening a new front in the forever wars which President Donald Trump previously vowed to end”.

As the war in the Middle East has dragged on with no clear end, Oman has stood out from other Gulf states in its increasing willingness to condemn and criticise the US, the closest and most important ally for the Gulf countries, accusing them of being a proxy for Israeli interests in the region.

In comments to reporters last Thursday, Albusaidi said the US was intent on causing irreversible damage to international law and helping Israel re-order the Middle East to its own benefit.

“Oman’s view is that the military attacks against Iran by the United States and Israel are illegal and that for as long as they continue to pursue hostilities, those states that launched this war are in breach of international law,” he said.