First, is Iran now set on having a nuclear weapon? It says not. But the most plausible interpretation of its behaviour is that it wants to put itself within easy reach of one.

Secondly, can diplomatic pressure persuade it to drop those ambitions? A plausible answer is that the United Nations might eventually persuade it to freeze its work — but almost certainly not to scrap what it has achieved.

On that view, the best interpretation of this week’s events is that Iran is pressing ahead as fast as it can so that, if it does ever strike a deal, it surrenders as little ground as possible.

Yesterday the countries that have most energetically tried to persuade Iran to leave the nuclear road joined together to condemn its action.

It was important for the hopes of any diplomatic pressure that Russia and China, both permanent members of the United Nations Security Council, added their voices to that declaration.

The United States, Britain and France, the other permanent members, have been vigorous in wanting to ratchet up pressure on Tehran, but Russia and China have held back. Iran has gone to great lengths to sign intricate and lucrative energy deals with Russia and China, and they stand to lose most if the UN moves towards sanctions.

Russia pointedly added yesterday that it believed that force could not resolve the dispute. Sergei Lavrov, the Foreign Minister, said that military plans “could create a dangerous explosive blaze in the Middle East, where there are already enough blazes”.

Wang Guangya, China’s UN Ambassador, said “to talk about military and other sanctions will not be helpful”.

Weekend reports in the US suggested that the Bush Administration was keeping the option of military action open, at least in theory, even though President Bush dismissed the talk as “wild speculation”.

Condoleezza Rice, the Secretary of State, said yesterday that the Security Council, which has told Tehran to halt all enrichment work by April 28, would need to “take strong steps to make certain (to) maintain the credibility of the international community”.

“When the Security Council reconvenes this month,” Ms Rice said: “I think it will be time for action. We can’t let this continue.”

Mohamed ElBaradei, Director-General of the International Atomic Energy Agency, the UN watchdog, will arrive in Tehran today to seek full co-operation with the Security Council and IAEA.

Many analysts have argued that the provocative timing of the move, in the middle of the 30-day period set by the council for freezing the work, is an attempt to secure Iran’s position, and present a fait accompli.

Iran is likely to argue that it cannot be expected to give up all of a programme showing steady technical progress. “They clearly have no intention of stopping”, Gary Samore, proliferation expert at the MacArthur Foundation in Chicago, said.

Mark Fitzpatrick, of the International Institute for Strategic Studies in London, argued that “negotiating with a country to roll back” a programme was rarely successful — witness the success of North Korea in holding on to its work in the face of intense international pressure.

European officials believe that the best chance for diplomacy may be to force Iran into the position of rejecting an offer that all members of the Security Council regard as self- evidently reasonable.

One version of this has been mooted by British officials — that the five permanent members of the council, plus Germany, offer a return to talks provided that Iran freezes its enrichment and submits to all IAEA inspections.

Iran’s move this week appears designed to make even that attempt look out of date.

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