Pentagon hawks have begun discussing military action against Iran to neutralize its nuclear weapons threat, including possible strikes on leadership, political and security targets.
With a deadline of today for Iran to begin an agreed freeze on enriching uranium, which can be used to produce nuclear weapons, sources have disclosed that the latest Pentagon gaming model for "neutralizing" Iran's nuclear threat involves strikes in support of regime change.
Although the US has made clear that it would seek sanctions against Iran through the UN should it not meet its obligations, rather than undertake military action, the new modelling at the Pentagon, with its shift in emphasis from suspected nuclear to political target lists, is causing deep anxiety among officials in the UK, France and Germany.
The International Atomic Energy Agency (IAEA) is due to meet on Thursday to decide whether to refer Iran to the UN Security Council for being in breach of non-proliferation measures.
Sources close to the Bush administration have warned that Tony Blair will have to choose between the EU's pursuit of the diplomatic track and a more hardline approach from the White House.
While George Bush clearly favors more stick and less carrot, it is not yet clear what the stick might be: US administration sources say targeted air strikes -- either by the US or Israel -- aimed at wiping out Iran's fledgling nuclear program would be difficult because of a lack of clear intelligence about where key components are located.
Despite America's attempt to turn up the heat on Iran, analysts remain deeply uncertain whether the increasingly bellicose noises which are coming from Bush administration figures represent a crude form of "megaphone" diplomacy designed to scare Iran into sticking to its side of the bargain, or evidence that Washington is leaning towards a new military adventure.
Details of the emerging Pentagon thinking have come as US officials have spent the past week turning up the pressure on Iran before the deal comes into force.
US officials are expected to meet European diplomats and IAEA officials to complain about Iran's continuing production of substantial quantities of uranium hexafluoride, which can be used in a weapons program.
Although not explicitly barred in the accord, US officials believe it amounts to a serious show of bad faith by Iran.
Under a pact reached by European countries and Iran last week, Iran is due to suspend all uranium enrichment, while it negotiates a deal in which it would receive trade incentives and peaceful nuclear technology.
Yesterday, the British Foreign Office tried to play down fears that Iran is already breaching the deal which was negotiated with the EU, insisting that the IAEA be allowed to issue its own verdict this week.
But government sources said the UK accepted that Iran had a complex and extensive nuclear program that could not be shut down overnight.
"There is a lot of speculation that is unfounded. Obviously there have been a lot of concerns in the past, but there's a deal on the table and we hope that they will stick with it," said one.