When President Mahmoud Ahmadinejad decided to go on his annual visit to New York this month, it probably seemed like a good idea at the time.

The Iranian leader, re-elected in June amid widespread allegations of vote rigging, desperately needed to restore credibility at home and abroad. With the results of the contested election confirmed by the authorities and his government sworn in last month, he may have concluded that opposition to his rule was weakening, not least because scores of his opponents had been arrested or intimidated. He probably calculated that turning up for the UN General Assembly, alongside President Obama, Gordon Brown and other leaders, would improve his standing on the world stage and make him look statesman-like at home.

Yesterday he may have regretted that decision, amid signs that the trip, scheduled for the middle of next week, may backfire.

Street protests by tens of thousands of opposition supporters in Tehran and other Iranian cities demonstrated that the challenge to his leadership is far from over. Similar protests are likely to dog him in New York. This time Iranian expatriates will probably be protesting alongside American Jews, angered at Mr Ahmadinejad’s repeated denial of the Holocaust and his prediction that Israel will soon cease to exist.

Although his remarks are not new, the atmosphere in the international community is a lot less forgiving. For a start, George W Bush no longer offers a tempting target for foreign leaders who like to portray America as the world’s aggressor.

President Obama, by contrast, has been far more conciliatory towards the Muslim world. He even offered publicly to reopen dialogue with Iran after 30 years — a gesture that has so far been rebuffed by the regime in Tehran.

A flurry of recent diplomatic moves in Europe may also make life more difficult for the Iranian leader. The Obama Administration this week unilaterally dropped America’s planned missile defence shield in eastern Europe. Although it was designed to prevent Iranian ballistic missiles attacking the West, it was regarded by Russia as a threat to its security.

The Kremlin is delighted with the American U-turn and will now be under pressure to return the favour when Iran’s controversial nuclear programme comes under the scrutiny of leading world powers — America, Britain, China, France, Germany and Russia.

So far Moscow has refused to support sanctions on Iran backed by Washington, London and Paris. It may, however, soften its position after the American move.

Certainly the much-anticipated defiant message Mr Ahmadinejad is preparing to deliver in New York could further isolate Iran and his beleaguered leadership.

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