U.S. Secretary of State John Kerry arrived in Moscow on Tuesday to try and narrow differences with Russian leader Vladimir Putin over the role of Syrian President Bashar al-Assad in any political transition and which rebel groups should be part of peace talks. 


Kerry will seek to prepare the ground for a third round of talks of world powers on Syria amid doubts over whether a meeting pencilled in for Friday in New York will go ahead. 


Russia's Foreign Ministry said late on Monday that Kerry and Russian Foreign Minister Sergei Lavrov agreed in a phone call on the need for specific preconditions to be met before any new meeting, throwing the timing into doubt. 


However, U.S. State Department spokesman Mark Toner s