MOSCOW - U.S. Secretary of State John Kerry sought in a visit to Moscow on Tuesday to make progress in narrowing differences with Russian leader Vladimir Putin over how to end the conflict in Syria.

At the start of a three-hour meeting with Russian Foreign Minister Sergei Lavrov, Kerry said he wanted to prepare the ground for a third round of talks of world powers on Syria, which is penciled in for Friday in New York.

It was unclear whether the meeting would go ahead without progress between Russia and the United States over the role of Syrian President Bashar al-Assad in any political transition and over which rebel groups should be part of peace talks.

Both these issues would be discussed with Putin at the Kremlin later in the day.

"I look forward to making real progress," Kerry said before his meeting with Lavrov, which was followed by a lunch.

"I think the world benefits when powerful nations with a long history with each other have the ability to be able to find common ground," he added.

Kerry told Lavrov: "Even when there have been differences between us we have been able to work effectively on specific issues."

Russia, one of Assad's staunchest allies, has launched a campaign of air strikes that it said targeted Islamic State militants but which also supported Assad's forces. The Kremlin says the Syrian people, and not external powers, should decide Assad's political fate.(Reuters)