Syrian forces fight their way into Palmyra, as Kerry and Putin hail thaw

US Secretary of State John Kerry met President Vladimir Putin in Moscow in an atmosphere that was noticeably more amiable than past meetings, reflecting new diplomacy the two Cold War superpowers have championed in recent weeks.

Both men expressed hope for more progress toward ending the fighting.

In Geneva, where the first peace talks involving President Bashar al-Assad's government and his foes began this month, the opposing sides were expected to sign on to a UN document reflecting some initial common ground.

The aim was to move toward discussing the divisive question of a political transition in Syria when the talks resume next month.

Moscow is the main ally of Assad's government, while Washington and other Western countries have backed foes trying to overthrow him during five years of civil war that has killed 250,000 people and led to the world's worst refugee crisis.

Both superpowers share a common enemy in Islamic State, the Sunni Muslim fighters who have declared a caliphate to rule over all Muslims from territory in Syria and Iraq.

After Russia intervened with air strikes to shore up Assad last year, Washington and Moscow have jointly sponsored a peace process that has produced the first sustained ceasefire of the war and the first negotiations involving the warring parties.

"The serious approach that we have been able to cooperate on has made a difference to the life of people in Syria and to the possibilities of making progress on peace," Kerry said at the start of talks with Putin in Moscow.

"The people of Syria and the people of the region have as a result been able to taste and smell the possibilities of what it means to have a huge reduction of violence and receive humanitarian assistance."

Putin, who has announced he is winding down Russia's military involvement in Syria, even offered warm words for US President Barack Obama, with whom his relations have sunk to a Cold War-era level of hostility since Washington imposed sanctions on Russia over its intervention in Ukraine in 2014.

"We understand that what we have been able to achieve on Syria has been possible only thanks to the position of the US top political leadership, President Obama," Putin said at his meeting with Kerry. "I very much hope that your visit will allow us to bring our positions closer on moving forward to solve the Syrian crisis and ... on Ukraine."

The US and Russian-sponsored ceasefire between Assad's government and his enemies does not cover Islamic State, allowing Damascus to ramp up its fight against the jihadists.