The only friendly neighbour is its client state, Lebanon.

While the conservatives in Iran may not be enthused about a US military presence on their doorstep, they have watched Washington take out of circulation three of the people they most fear in the world: Mullah Omar, Osama bin Laden and Saddam Hoseyn.

There is no such mitigation for Syria, which loses economically as well as politically.

Syria was one of the big beneficiaries of the failing containment policy that led the US to war.

The moribund Syrian economy was gaining much from its illicit trade with Iraq.

Within a few years of reopening a pipeline in 2000 to take smuggled oil out of Iraq, Syrian trade with Iraq exploded to more than $2bn (£1.3bn) annually.

That pipeline was shut down by US troops this week; and the prospect for other smuggling has collapsed with the expected end to the United Nations embargo.

But co-operation appears to have continued well into the military campaign.

Yet why did Damascus court US wrath by co-operating with a regime in its death throes, given the explicit US warnings for it not to interfere?

And how does this sit with Syria's apparent intelligence co-operation with Washington about al-Qaeda that, in the words of State Department official Richard Erdman, "saved American lives"?

Scott Lasensky of the Council on Foreign Relations advances three possible explanations:

* Bashar al-Assad, who took over from his father as president in 2000, is less experienced, less cautious and is looking for a way to fill a leadership vacuum in the Arab world.

* He may not be fully in control of his administration. This may be why the US chose to respond in such a public manner, making sure every element of the regime got the message.

* Economic reasons. Iraqi chequebooks go a long way in Syria.

The younger Assad certainly never shared his father's deep animosity towards Mr Hoseyn - he even became friendly with Qusay Hoseyn, says Kenneth Pollack, a former CIA analyst.

Mr Lasensky says Washington's warnings this monthhave to be seen largely in the context of Iraq.

The first signs of US anger at Damascus came in the thick of the campaign.

The night-vision goggles apparently being smuggled from Syria would have neutralised a key US advantage in night fighting.

This could have complicated the task of taking Baghdad and could have helped Iraq if it unleashed chemical weapons, which probably would have been used at night.

He says subsequent warnings were meant to carry a message to the Syrians not to interfere with Iraqi reconstruction.

They says that will not simply be about putting pressure on Israel.

In spite of talk of sanctions, US economic leverage over Damascus is limited.

US aid and military sales are barred by law, US flights do not go to Damascus, trade is small and there is just one US oil company, Conoco-Phillips, there. And although the Syrian regime is deeply disliked by the Bush administration, not least for its support of Hezbollah, the Lebanese guerrilla group, the military option does not appear to be on the table.

Editor’s note: Some Phonetisation of names and highlights are by IPS