Iranian foreign minister says America has 'lost its wisdom and prudence' as tensions mount over Tehran's enrichment efforts

Iran has warned the US not to set the two countries on a collision course over Tehran's nuclear enrichment programme, as diplomatic tensions reflected growing concern that the Middle East might be on the verge of new conflict.

The Iranian foreign minister, Ali Akbar Salehi, spoke amid reports that the Israeli prime minister, Binyamin Netanyahu, has been trying to rally support within his country for an attack.

The Guardian revealed that the UK was advancing contingency plans for joining American forces in a possible air and sea campaign against military bases in Iran.

The revelations led to Nato insisting on Thursday that it would play no part in any military action, and provoked the rebuke from Salehi, who insisted that any attack by either Israel or the US would provoke immediate retaliation. He also accused Washington of recklessness.

"The US has unfortunately lost its wisdom and prudence in dealing with international issues," he told reporters during a visit to Libya. "Of course we are prepared for the worst, but we hope that they think twice before they put themselves on a collision course with Iran."

In a separate interview with a Turkish newspaper, Salehi claimed Tehran was ready for war with Israel. "We have been hearing threats from Israel for eight years. Our nation is a united nation … such threats are not new to us," he said. "We are very sure of ourselves. We can defend our country."

The pressure on Iran has been building since allegations surfaced of a plot to assassinate the Saudi ambassador to Washington. The White House insists Tehran was behind the plot, but the Iranian regime has denied that.

The episode added to US concerns about Iran's nuclear enrichment programme and the increasing belligerence of its regime. Intelligence suggests that some of the Iranian centrifuges that can produce weapons-grade uranium are being hidden inside a fortified military base in Qom, about 100 miles south-west of Tehran.

The International Atomic Energy Authority will next week deliver its latest bulletin on Iran's nuclear programme and is expected to provide fresh evidence of covert plans to engineer warheads.

The Israeli defence minister, Ehud Barak, said to be one of those pushing for an early attack on Iran, was in London on Thursday for talks with David Cameron's national security adviser, Sir Peter Ricketts, the foreign secretary, William Hague, and the new defence secretary, Philip Hammond.

Hague said the meeting had given them a chance to discuss "shared concerns such as … the threat posed by Iran's nuclear programme". Downing Street said "all options are on the table" for dealing with Iran unless it truly abandons any plans to arm itself with nuclear weapons.

Though Britain says its policy on the issue has not changed, the Guardian disclosed that British military planners were now having to turn contingency plans into practical steps, such as considering when to deploy Royal Navy submarines equipped with Tomahawk cruise missiles to the region, in case Barack Obama bows to pressure to launch missile strikes against Iranian bases.

Although Iran has insisted it is only developing nuclear energy, Whitehall officials believe the regime will have hidden all it needs to build weapons inside fortified compounds within 12 months – adding a sense of urgency to diplomatic efforts.

The Nato secretary general, Anders Fogh Rasmussen, called for political and diplomatic efforts to resolve the growing crisis. He insisted that Nato would not be drawn into any military action.

"Let me stress that Nato has no intention whatsoever to intervene in Iran, and Nato is not engaged as an alliance in the Iran question," he said.

Villy Søvndal, the new Danish foreign minister,said he could not see any circumstances in which his country would join a military effort against Iran, as it had done in Libya and Afghanistan. "The difference between Libya and Iran is that I could never imagine a UN resolution behind a military attack on Iran. There would be no regional backup. That would be one of the most impossible military missions.

"Of course, you can bomb some buildings and equipment and maybe you could delay for a period of one or two years. But I can no see any situation in which Denmark would participate. It would produce so much instability … you could also end in a situation where you strengthen the present Iranian regime."

In Israel, the row over whether to launch strikes against Iran continued, with Netanyahu reportedly ordering an investigation into alleged leaks of plans to attack nuclear facilities.

According to the Kuwaiti newspaper al-Jarida, the main suspects are the former heads of the Mossad and the Shin Bet, respectively Israel's foreign and domestic intelligence agencies. Netanyahu is said to believe that the two chiefs, Meir Dagan and Yuval Diskin, wanted to disrupt plans being drawn up by him and Barak to hit Iranian nuclear sites.

Both Dagan and Diskin oppose military action against Iran unless all other options – primarily international diplomatic pressure and perhaps sabotage – have been exhausted.

In January the recently retired Dagan, a hawk when he was running the Mossad, called an attack on Iran "the stupidest idea" he had ever heard. The Kuwaiti newspaper has a track record of running stories based on apparently high-level leaks from Israeli officials.

Even well-informed Israeli observers admit to being confused about what is going on behind the scenes.

"It seems that only Netanyahu and Barak know, and maybe even they haven't decided," said Amos Harel and Avi Issacharoff, both respected writers for the newspaper Haaretz.

"While many people say Netanyahu and Barak are conducting sophisticated psychological warfare and don't intend to launch a military operation, top officials … are still afraid."

The debate in Israel intensified further on Wednesday when Israel test-fired a missile capable of carrying a nuclear warhead to Iran.