A coalition of countries that could launch military action in Syria is taking shape, following the alleged deadly chemical weapons attack last week that the West has blamed on the regime.
The United States would no doubt spearhead any intervention, France and Britain would participate and nations in the region such as Turkey would provide support.
Russia -- a permanent member of the United Nations Security Council and a Syria ally -- opposes military action, which means any such intervention would take place without the world body's green light.
The countries, gathered together as part of a "coalition of the willing", would take part in an operation aimed at punishing the regime of Bashar al-Assad for the alleged chemical attack with targeted strikes, but not aimed at overthrowing the government.
A one-off operation is unlikely to be met with major political opposition in the three countries currently most involved: the United States, France and Britain.
The US president has the power to decide to launch air strikes without the agreement of Congress, which is currently on summer break and is only due to reconvene on September 9.
But he must inform Congress and Barack Obama is already actively consulting lawmakers.
In Britain, Prime Minister David Cameron has said he will recall lawmakers from their summer break on Thursday to vote on a "proportionate response" to the alleged gas attack.
In France, where President Francois Hollande has called for a "common response" from Western countries to "an intolerable act", a one-off military intervention does not need parliamentary approval.
Germany, meanwhile, is not considering military participation less than one month before crucial legislative elections.
But Foreign Minister Guido Westerwelle has said his country would support potential action against the Syrian regime.
Italy has rejected any military intervention in Syria without the approval of the UN Security Council, where Russia is likely to block any such move.
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But Turkey, which as a neighbour of Syria has taken in around 500,000 refugees as well as army defectors, has said it is ready to join an international coalition even without UN consensus.
Saudi Arabia, Qatar and the United Arab Emirates (UAE), all of which support the Syrian rebellion, have been consulted by the West over a potential military operation.
Jordan, which has also taken in some 500,000 refugees from Syria and fears a rise in Islamic extremism, has said it will not be a "launchpad" for military intervention in Syria.
Washington's top regional ally Israel, which is believed to have carried out several strikes in neighbouring Syria since the start of the crisis, has warned it would retaliate "fiercely" if Damascus responded to international military action by striking the Jewish state.
The countries involved in a potential operation already have significant air and naval military capabilities in the region.
Limited action -- the option most favoured by experts at this stage -- could consist in targeted strikes by missiles launched from the sea against ammunition depots or strategic infrastructure.
The United States has four destroyers in the Mediterranean Sea (USS Mahan, Ramage, Barry, Gravely) carrying Tomahawk long-range cruise missiles.
It can also count on two air bases in Turkey, in Izmir and Incirlik.
Several ships belonging to the 26th Marine Expeditionary Unit are docked in a port in the UAE, and the Truman aircraft carrier is also currently in the north of the Indian Ocean.
France, meanwhile, has submarines equipped with cruise missiles that can also be launched by planes.
It has frigates in the Mediterranean that can carry helicopters, and also has fighter planes in Djibouti (seven Mirage 2000s) and Abu Dhabi (six Rafales).
Britain can mobilise a cruise missile submarine, which would be its main contribution to the operation, experts say.
British ships are also currently in the Mediterranean: the HMS Illustrious, a helicopter carrier, and two Type-23 frigates, but none of these can launch missiles. The Royal Air Force also has a base in Cyprus.
Turkey has Patriot air defence missiles stationed on the border with Syria, set up by the US, German and Dutch armies to protect it against potential Syrian strikes.
Italy, finally, has not ruled out allowing its allies to use its air bases, despite its opposition to an intervention without UN consensus.