Con Coughlin:

Tehran’s regime is driven by a religious extremism that is undermining the entire world’s stability

What a difference a year makes. When US President Donald Trump made his first appearance at the UN Security Council last September, his confrontational attitude towards North Korea raised widespread fears that hostilities were about to be renewed on the Korean peninsula.

Then, to everyone’s surprise, Mr Trump achieved the breakthrough that had eluded American diplomats for two decades or more. Rather than risk the prospect of an all-out war with the US over his country’s ability to develop nuclear weapons, North Korean dictator Kim Jong-un instead agreed to meet the US President in person to settle their differences, with the summit eventually taking place in Singapore. And while it would be foolhardy to believe Mr Trump’s high-risk strategy has resolved the North Korean issue once and for all (for all the talk, Pyongyang still retains a powerful nuclear weapons arsenal) there can be no doubting that there has been a marked improvement in relations between North and South Korea.

Having sorted out one rogue state, Mr Trump now seems intent on adopting a similar approach towards Iran, another nation that Washington has long regarded as playing a lead role in what the Bush administration termed the “axis of evil”.

To this end, the president is using his appearance at this year’s gathering of foreign dignitaries, where he will have the rare privilege of addressing the Security Council later today, to concentrate his fire on Tehran. The tone was set as Mr Trump addressed the full assembly yesterday, when he revealed he had turned down a request by his Iranian counterpart, Hassan Rouhani, for a face-to-face meeting. “I am sure he is a lovely man”, the president tweeted on his decision to spurn the advance, adding that “Iran has to change its tune” before he would agree to such a meeting.

Nor did the president leave anyone in any doubt about how he views the Iranian regime. The country was “the world’s leading sponsor of terrorism”, which had used the “windfall” it received as a result of signing the controversial nuclear deal in 2015 to increase its military budget by 40 per cent. The extra money had been used to finance terrorism and “fund havoc and slaughter in Syria and Yemen”.

The delegates may have laughed at Mr Trump’s boast that his presidency had achieved more than any other administration, but the tone of his rebuke to Iran demonstrates that he is deadly serious about subjecting Tehran to the same relentless diplomatic, economic and military pressure that eventually brought Kim to the negotiating table.

This hawkish approach may have succeeded in defusing tensions with North Korea. But persuading the ayatollahs to mend their ways is an entirely different proposition, not least because the regime is driven by religious extremism, not political ideology.

Iran’s commitment, moreover, to exporting the principles of its Islamic revolution throughout the Muslim world means that, unlike the North Koreans, much of the regime’s energy is invested in meddling in the affairs of other states. Lebanon, Syria, Iraq, Yemen and the Gulf states: all have been subjected to the unwelcome attentions of Iran’s Revolutionary Guard Corps, to the extent that any future confrontation between the US and Iran is unlikely to be confined within Iran’s borders.

This week’s announcement by Moscow – that it is deploying its state-of-the-art S-300 anti-aircraft missile system to Syria – provides a good example of how Iran’s overseas interference creates further instability in the region. The Russians announced the upgrade after their Syrian allies accidentally shot down a Russian aircraft, believing it to be an Israeli warplane carrying out a bombing raid on an Iranian missile factory. If the Iranians had not been operating in Syria, the Israelis would have no reason to attack the country – and the Russians would not feel compelled to upgrade their military presence.

The Trump administration’s determination to confront the ayatollahs, moreover, deserves the support of allies, such as Britain, who have much to lose if the spread of Iran’s pernicious influence is not contained.

Foreign Secretary Jeremy Hunt has, to date, been admirably robust in his public criticism of Tehran over its treatment of Nazanin Zaghari-ratcliffe, the British-iranian woman jailed in Tehran on false spying charges. He should now follow this up by persuading his cabinet colleagues that the time has come for Britain to join the US in withdrawing from the nuclear deal.

Previously the Government has argued that sticking with the deal is the best way to encourage Tehran to be more responsible. But, as its actions in Syria and elsewhere have shown, the ayatollahs are interested only in sowing discord, not harmony. The best way to bring them to their senses is for Britain and other European powers to give the American president their unequivocal support.