ST PETERSBURG: US Secretary of State Hillary Rodham Clinton and Russian Foreign Minister Sergey Lavrov were heading for a face-to-face showdown over Syria on Friday as major powers prepared for a weekend conference to hash out a political transition plan for the country.

On the eve of Saturday’s conference aimed at ending 16 months of brutal violence in Syria, Hillary and Lavrov were to meet in St Petersburg in a bid to iron out deep differences over the transition plan being pushed by UN envoy Kofi Annan that calls for the formation of a national unity government that would oversee the drafting of a new constitution and elections.

US officials are adamant that the plan will not allow Syrian President Bashar Assad to remain in power at the top of the transitional government, but Russia insists that outsiders cannot dictate the ultimate solution or the composition of the interim administration.

Annan's plan would allow some members of the current regime to stay in place but would exclude those deemed to be counterproductive or destructive to the transition process, which would be Syrian led, according to diplomats familiar with the proposal. It does not explicitly bar Assad, but the US and other western powers who will participate in the conference in Geneva say that is implicit.

The difference in interpretation could prove its unravelling and Hillary hopes to press Lavrov on the point at their meeting and over dinner following a gathering of Asia-Pacific foreign ministers that Lavrov is hosting in St Petersburg.