By Jonathan Beale
BBC state department correspondent
Iran's promise to back Syria against threats from America will not unduly alarm the US administration.
Mr Bush may link Iran and Syria rhetorically but differences remain
After all, President George W Bush has been lumping them together in his more recent criticisms.
But there are significant differences between the rhetoric US administration officials use when referring to Iran and Syria and to the policy the Americans pursue towards them.
The US sees Iran as the bigger threat in the long term, but administration officials also see Syria causing more problems in the short term by destabilising Middle East peace efforts.
Alike but different
First the similarities. President Bush has accused both countries of failing to tackle the insurgency in Iraq.
Look at the language the president used in his State of the Union address earlier this month.
He said: "Iran aggressively pursues these weapons [of mass destruction] and exports terror, while an unelected few repress the Iranian's people's hope for freedom".
His comments on Syria were in a similar vein: "We expect the Syrian government to end all support for terror and open the door to freedom."
Syria and Iran said they were facing "numerous challenges"
There are, however, important differences.
The rhetoric towards Iran is more strident. That is because the US believes Iran is on the path to manufacturing nuclear weapons and hence why Iran is included as part of "the axis of evil".
Syria was not included.
The US administration also believes that the rulers in Tehran are more repressive.
In other words, they are a bigger obstacle to spreading the president's global goal of spreading freedom.
Differences in diplomacy
There is also a significant difference in diplomatic relations.
Though relations are now strained to breaking point, the US has been prepared to deal directly with Damascus.
There was a limited amount of intelligence co-operation following the attacks of 11 September 2001.
President Bush's decision to recall his ambassador in Damascus following the Beirut bombing shows that the relationship is getting much worse.
But there has at least been a limited dialogue while there is almost none with Iran. For the time being the US is leaving that to the Europeans.
So the US still sees Iran as the bigger threat but in many ways Syria presents a more immediate problem.
Both President Bush and Secretary of State Condoleezza Rice have expressed a genuine desire to help create a peaceful Palestinian state.
The US believes Iran's nuclear ambitions pose a bigger threat than Syria
Syria, though, is seen as a destabilising force in the Middle East.
The US administration has already implemented, with the impetus coming from politicians on Capitol Hill, the Syria Accountability Act.
The US has enforced sanctions against Syria because it believes Damascus has failed to stop Palestinian militants from crossing the border into Israel.
The killing of Rafik Hariri in Lebanon has added to the US pressure on Damascus. America wants Syria to get its troops out of Lebanon.
In the end the US hopes that it can still influence Syria to change course, with the help of the international community.
That optimism is almost absent on Iran.
While Iran has been quick to rush to Syria's defence in this angry war of words, Syria does not seem as anxious to become part of an anti-American coalition.