David Miliband has raised questions over Barack Obama’s policy on Iran, which officials in Washington and Europe fear threatens to undermine the tough stance adopted by the West towards Tehran over recent years.

The Foreign Secretary, on his visit to the US this week, has held talks with all three presidential campaigns, including those of Hillary Clinton and John McCain.

But when he met Mr Obama’s team of foreign policy advisers on Wednesday, Mr Miliband is understood to have queried the presumptive Democratic nominee’s declared willingness to meet leaders from rogue states such as Iran.

They also discussed trade — with Mr Obama advisers saying that they still intended to renegotiate deals such as Nafta — and how much European support there would be for a US military surge in Afghanistan.

British intelligence chiefs are understood to have identified Iranian nuclear proliferation as the second greatest security threat, behind Islamic terrorism but ahead of renewed aggression from Russia.

There is also deep concern about Iran’s support for Iraqi Shia militias or terrorist groups such as Hamas and Hezbollah. “The role of Iran as a source of instability in the region is undoubtedly a concern,” Mr Miliband said this week. “No one can watch armed militias coming on to the streets in defiance of UN resolutions with equanimity.”

Exact accounts of the conversation with Mr Obama differ and there is certainly acute anxiety on the part of the British not to be seen as stoking political controversy in America’s presidential elections. In the past week Mr McCain has repeatedly hammered Mr Obama for what he claims is a “naive” commitment to hold direct talks with foreign dictators.

In a televised debate last summer, Mr Obama was asked if he would be willing to meet the leaders of countries such as Iran and Cuba without preconditions during his first year in office. He replied: “I would.” But this week he appeared to pull back, saying he would still be willing to meet Iranian leaders but not before what he described as “preparations” — and not necessarily with President Ahmadinejad.

Nevertheless, Mr Obama says that “tough but engaged diplomacy” — of the type carried out by President Kennedy or President Reagan with the Soviet Union — would represent “a different approach, a different philosophy” to the “failed Iran policy” of the current administration.

Mr Miliband, in a press conference with US Secretary of State Condoleezza Rice, reiterated Britain’s support for the united front on Iran adopted by the US and its European allies, which he believes is beginning to pay dividends. “Our position, jointly, has always been that as long as Iran exercises responsibilities, then it will be able to forge a more productive and positive relationship with the international community,” Mr Miliband said.

An aide later told The Times that the Foreign Secretary was being very careful to avoid direct criticism of any presidential candidate’s positions. But the same source added: “We know Obama wants to engage more, but we don’t know what route he will take or what he means by ‘no pre-conditions’. It has not unravelled yet and, when it does, we will be able to see where it converges or conflicts with what we’re doing.”

A Foreign Office spokesman later said: “I just want to stress that David Miliband is not confused about Obama’s policy. It would be quite wrong to say that.”

Mr McCain’s foreign policy chief, Randy Scheunemann, would not comment on his own meetings with Mr Miliband. But he said: “Obama’s position is obviously different to that of Britain and France. Otherwise Prime Minister Brown and President Sarkozy would have already met the President of Iran without conditions.

Although Britain — unlike the US — maintains diplomatic relations with Iran, the West has been more or less united in seeking to isolate the Iranian leadership. The US, Britain, France and to some extent Germany have pressed for tighter sanctions against Iran, including measures directed against the country’s ruling elite, for failing to comply with UN resolutions calling for a halt to its uranium enrichment programme.

British intelligence chiefs are understood to have identified Iranian nuclear proliferation as the second greatest security threat, behind Islamic terrorism but ahead of renewed aggression from Russia.

There is also deep concern about Iran’s support for Iraqi Shia militias or terrorist groups such as Hamas and Hezbollah.

“The role of Iran as a source of instability in the region is undoubtedly a concern,” Mr Miliband said this week. “No one can watch armed militias coming on to the streets in defiance of UN resolutions with equanimity.”

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