Barack Obama is unlikely to have much trouble mustering a Nato coalition of the willing if Washington opts for military intervention in Syria in response to the alleged chemical weapons atrocities by the Assad regime.

There is, however, no prospect of a UN mandate for international military action over Syria – with the Kremlin, enraged at what it saw as abuse of a UN mandate to topple Muammar Gaddafi in Libya, certain to keep wielding its veto.

Turkey, which accounts for Nato's second largest army after the US, and which is on the frontline with Syria, bearing the brunt of the massive refugee crisis, is already a key conduit for arms supplies to, and a safe haven for, the sundry groups of fighters at war with Damascus.

It has been the loudest critic of the Assad regime, clamouring for the west to do more. In any international coalition Turkey would be likely to play a key role – with a potential impact on the country's own ethnic balance, especially the relations between the Sunni Muslim majority and the sizeable Alevi minority concentrated in the south near the Syrian border.

Britain and France, the EU's only military powers with the capacity and will to project military muscle abroad, look certain to line up with the US.

Since last week's reports of chemical weapons use, Laurent Fabius, the French foreign minister, has been among the loudest arguing that "something must be done".

On Sunday he repeated, while visiting Israel, France's demand for a strong response to the chemical weapons allegations. In meetings last week that echoed the run-up to the Anglo-French-led campaign in Libya, Fabius also discussed options with William Hague, the British foreign secretary.

Israel, another neighbour with a huge interest in Syria, is also likely to support the US, although intensely worried about the form and substance of a post-Assad Syria.

Shimon Peres, the Israeli president, after meeting Fabius, on Sunday called for an international operation to remove chemical weapons from Syria.

"The time has come for a joint effort to remove all the chemical weapons from Syria. They cannot remain there either in the hands of Assad or of others. I understand the problems and doubts … but the moral call is superior to any strategic considerations."

France and Britain took the lead in the international effort to unseat Gaddafi in Libya, citing the risks of a bloodbath attending the potential fall of rebel-held city, Benghazi. The French, with British support, also intervened militarily last year in Mali to preempt the fall of much of the country to Islamist militias.

Since the start of the year Britain and France have led the campaign to alter the EU sanctions regime against Syria to lift the arms embargo on rebel forces.

This weekend about 400 tonnes of arms went to the rebels across the Turkish border in what was described as one of the biggest weapons shipments ever.

London and Paris were isolated, however, in their calls for a common European position on lifting the arms embargo, and it is likely that a campaign of military strikes aimed at weakening the Assad regime and bolstering the opposition will trigger deep divisions in the EU and at Nato HQ in Brussels where the Americans would push for the broadest consensus supporting intervention if they decided to act militarily.

Germany is unlikely to back intervention, especially in the run-up to next month's general election. That opposition might subside if Angela Merkel, the chancellor, wins a third term, as expected, but she may be forced to make her position clear before the ballot.

Poland, the biggest EU military power in the east, denounced last week's attack on civilians in Syria as a clear breach of international law, suggesting it would have little reservation about getting involved or at least supporting others.

Given the absence of a UN mandate because of a split security council, the 1999 Nato Kosovo intervention would give the most apt precedent for action, on grounds of humanitarian intervention.

Analysts and diplomats say the US will not want for justification for intervention if the White House decides on using force in Syria.