The eruption of civil conflict in Syria in 2011 very quickly provoked a deep split in the international community over which side to back and what outcome to seek.
With Syria regarded as the world's most pressing crisis, the US and Russia, along with other permanent members of the UN Security Council, Turkey and Arab states, have attempted to resolve their differences.
Their Geneva Communique, which calls for a transitional government based on "mutual consent", has become the basis for peace talks in the Swiss city. But it is clear the sides have different interpretations of the plan, and have so far failed to achieve a breakthrough.
US
The United States has been one of the most prominent advocates of firm action against the Syrian government, which it has accused of using chemical weapons and other atrocities.
In September 2013 President Barack Obama sought Congressional support for military action but postponed the vote - which was not certain to pass - when Syria indicated it would surrender its chemical stockpile.
Although it has stopped saying so, the US wants Bashar al-Assad out of power, and is pushing for the transitional government called for in the Geneva communique.
It is backing Syria's "moderate opposition" with "non-lethal" assistance, including communications equipment, generators, and office supplies - but is also believed to be supplying light weapons.