By Colin Freeman/ The Telegraph

Details remain sketchy, but it is thought it would involve a limited no-fly zone extending 25 miles into Syria, enforced by US aircraft flown from Jordanian bases.

The ground work for such a buffer zone have been in place since last year, when a detachment of 150 US troops moved into Jordan to help deal with contingencies arising from the massive influx of Syrian refugees, and to help secure Syria's chemical weapons stocks were President Bashar al-Assad's regime to suddenly collapse.

Should that buffer zone now be enacted, it will once again put small, pro-Western Jordan directly into the crossfire of a major Middle Eastern conflict. Jordan's urbane, Sandhurst-educated ruler, King Abdullah II, has already angered President Assad by leading Arab calls for him to step down, warning in late 2011 that an orderly transition was in the country's best interests. If the king were now to host what could be the "game-changing" operation to remove Mr Assad by force, it could invite serious retaliation, possibly in the form of terrorist attacks by Hezbollah militants allied to Mr Assad.

Jordan has already paid that kind of price in the past. Following the US invasion of Iraq, al-Qaeda mounted a series of devastating bomb attacks at three luxury hotels in the Jordanian capital, Amman, killing 56 people. The 2005 attacks were in retaliation for Jordan hosting training centres for the new Iraqi army and police, and for becoming a de facto transit base for much of the vast civilian operation in support of the US occupation. While the bombs were targeted at hotels favoured by Westerners, most of the victims were locals, who later dubbed it "Jordan's 9-11". Public outrage at the attacks is reported to have led Jordan's intelligence chiefs to help the US hunt down the then leader of al-Qaeda in Iraq, Jordanian-born Abu Musab al Zarqawi, who was killed in 2006.

For King Abdullah, the perils of direct involvement in the Syrian conflict must be weighed against the equal risks of simply letting the conflict drag on. Already, his country is a temporary home for up to half a million Syrian refugees, and a semi-permanent home for between 50,000 and half a million Iraqi refugees (precise figures are disputed). On top of that are nearly nearly two million Palestinian refugees who have fled there since the Arab-Israeli war of 1967. The recent arrivals have put a heavy added strain on Jordan, which is already struggling with high unemployment and huge water shortages, not to mention demands for an Arab Spring of its own to end King Abdullah's monarchy.

A series of pre-emptive reforms by the royal household has taken the sting out of those demands - for now at least. But in the capricious world of Middle Eastern politics, playing a military role in bringing about a neighbour's downfall - even that of someone as unpopular as President Assad - is a complication that King Abdullah could do without.