The United States and Russia need to find "common ground" to end Syria's civil war and restore stability in eastern Ukraine, US secretary of state John Kerry has said.
Opening talks in Moscow with Russian foreign minister Sergey Lavrov before seeing President Vladimir Putin, Mr Kerry said the world benefits when great powers agree in their approaches to major crises.
"Even when there have been differences between us, we have been able to work effectively on specific issues," he said as he began what are expected to be difficult discussions in the Russian capital.
"Today, I hope we can find some common ground."
Russia and the US are at odds over the mechanics of a political transition aimed at halting the war in Syria, as well as the military approach to fighting Islamic State (IS).
The results of the meetings will determine whether or not a new international diplomatic conference on Syria will go ahead as planned at the United Nations on Friday.
On Ukraine, the two countries are split over the implementation of a February agreement meant to end hostilities between the Kiev government and Russian-backed separatists in the eastern part of the country.
Mr Lavrov noted "outstanding issues" with the US on the Syrian political transition that is supposed to bring representatives of Syrian president Bashar Assad's government together with the opposition for negotiations by early January.
He said the US should use its influence with the government in Kiev to settle the conflict with the separatists in Ukraine by respecting a shaky ceasefire and moving ahead with political reforms.
Mr Kerry praised Moscow for having been "a significant contributor to the progress that we have been able to make" on Syria, and said the US and Russia both believe Islamic State must be eliminated.
He said: "Russia and the United States agree that this is a threat to everybody, to every country.
"They are the worst of terrorists. They attack culture and history and all decency. It leaves no choice but for civilised nations to stand together, to fight and destroy them."
However, ahead of his arrival, Russia's foreign ministry said Moscow would be looking for a "revision" in US policy "dividing terrorists into 'bad' and 'good' ones".
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