By Paul Reynolds
World Affairs correspondent, BBC News website
President Bush describing the State of the Union
American accusations against Iran are becoming more specific by the day, raising a question about how far this confrontation will go.
The charges are on two fronts - the first concerns alleged Iranian activities in Iraq (and in Lebanon) and the second is about Iran's nuclear programme.
The latest charge over Iraq, from Under Secretary of State Nicholas Burns, is that members of the Iranian Revolutionary Guard had been arrested there. "They're people who are engaged in sectarian warfare," he told the BBC.
He also re-stated the accusation that Iran was supplying technology for the shaped charges that were being used by Shia attackers on US and British forces.
Public criticism of Iran was one of the notable features of President Bush's State of the Union speech on 23 January.
A second aircraft carrier is now in the Gulf in what Vice-President Cheney said was a "strong signal" to Iran.
However Mr Bush has played down suggestions that a US attack on Iran is in preparation.
What does appear to be in force right now is a new harder-edged diplomacy, one aimed at further isolating Iran, with the ultimate hope perhaps that there will be a change of government.
Whether such an approach will in due course develop into something military remains to be seen.
References to Iran ran like a drum beat through the State of the Union speech, adding a wider element to the president's appeal for support for what he called his "new strategy" in Iraq.
He accused the "regime" in Iran of arming "terrorists like Hezbollah" and of directing "Shia extremists" in Iraq.
He raised the prospect of a larger conflict in the Middle East in which Iran would be central.
"If American forces step back before Baghdad is secure, the Iraqi government would be overrun by extremists on all sides," he said.
"We could expect an epic battle between Shia extremists backed by Iran, and Sunni extremists aided by al-Qaeda and supporters of the old regime.
"A contagion of violence could spill out across the country - and in time, the entire region could be drawn into the conflict."
And he did not leave out the nuclear issue: "The world will not allow the regime in Tehran to acquire nuclear weapons."
He referred only to the "regime" in Iran, not the government.
Such rhetoric is used partly to lay the blame for the chaos in Iraq on others but it is not just rhetoric. The State of the Union speech is a carefully considered declaration.
The new chairman of the Senate Intelligence Committee Senator John Rockefeller, a Democrat, has spoken out against the verbal attacks on Iran and compared them to what happened before the invasion of Iraq in 2003.
"To be quite honest, I'm a little concerned that it's Iraq again," Senator Rockefeller told the New York Times.
The anti-Iran trend in the administration was already evident when Mr Bush announced the increase in troops in Iraq on 10 January. In that speech he rejected the recommendations of the advisory Iraq Study Group that the United States should engage diplomatically with Iran (and Syria).
Instead he accused Iran and Syria of "allowing terrorists and insurgents to use their territory to move in and out of Iraq".
US failure in Iraq, he claimed, would have a consequence: "Iran would be emboldened in its pursuit of nuclear weapons."
And he added: "We will work with others to prevent Iran from gaining nuclear weapons and dominating the region."
That phrase "will work with others" is primarily a reference to the UN Security Council which has imposed sanctions on Iran, aimed at preventing it from getting technology useful for its nuclear enrichment and missile programmes.
The line from the White House, as expressed recently by the National Security Adviser Stephen Hadley, is that the US is seeking a diplomatic solution.
Asked on ABC television if the US was preparing an attack on Iran, he replied: "No, the president has said very clearly that the issues we have with Iran should be solved diplomatically."
This may be true but such a formulation does not rule out a future decision to move from a diplomatic approach to a military one, if diplomacy is held to have failed.
The mood in the administration coincides with some strong talk in Israel about the dangers from Iran.
The Israeli Likud party leader Binyamin Netanyahu has called the Iranian government "genocidal" and has said: "No-one will come to defend the Jews if they do not defend themselves."
Iran's president has dismissed the Security Council resolution
An example of the fears in Israel was a remarkable recent article in the Jerusalem Post by the Israeli historian Benny Morris, who raised the spectre of "the second Holocaust".
"One bright morning, in five or 10 years, perhaps during a regional crisis, perhaps out of
the blue, a day or a year or five years after Iran's acquisition of the Bomb, the mullahs in Qom will convene in secret session, under a portrait of the steely-eyed Ayatollah Khomeini, and give President
Mahmoud Ahmadinejad, by then in his second or third term, the go-ahead," he wrote.
"With a country the size and shape of Israel (an elongated 20,000 sq km), probably four or five hits will suffice: No more Israel."
Iran itself continues its dual policy of developing enrichment and denying any intention of using that expertise to build a bomb.
There are signs that some in Iran are worried about the combative approach of President Ahmadinejad.
A critical cleric, Grand Ayatollah Hussein Ali Montazeri, said: "One has to deal with the enemy with wisdom. We should not provoke the enemy, otherwise the country will be faced with problems."
Not that President Ahmadinejad is impressed. He dismisses the Security Council resolution as "born dead".
He states that Iran's efforts to enrich uranium are an expression of its right to develop nuclear power under the Nuclear Non-Proliferation Treaty of which it is a member.
Under the treaty, non-nuclear weapons states area are allowed to acquire nuclear technology for civil purposes but commit themselves not to build a bomb.