Washington is relying on the Kremlin to drag Russian ally Bashar al-Assad to the negotiating table for talks with his rebel opponents to end Syria's vicious civil war.
In turn, US ally Saudi Arabia is putting together a rebel coalition that would sit down with Assad's negotiating team, sign a ceasefire and start a political dialogue.
Looming over the effort to end the bloody four-and-a-half year civil war is the threat posed by the Islamic State group to spread the carnage beyond Syria's borders.
The hope is that if the regime and the rebels can agree a ceasefire then they, Russia and a US-led coalition of Western and Arab allies can focus their fire on IS.
Washington and Moscow are the key powers in the process, leading talks through the 17-nation International Syrian Support Group in cooperation with the United Nations.
Kerry and the UN envoy for Syria, Staffan de Mistura, want to hold the next round of ISSG talks on Friday in New York, but Moscow has so far refused to confirm the date.
At issue is the Saudi-mediated rebel delegation and a separate effort by Jordan to draw up a list of Syrian groups deemed "terrorists" and barred from the talks.
Moscow said on Monday that Friday's talks should not take place until both the rebel representation and the terror blacklist are agreed upon by all parties.
- US frustration -
But Washington insists it is vitally important to maintain the momentum of the process rather than squabbling over the detail, fearing that Putin is trying to buy Assad time.
"It is our expectation that this meeting will go forward on Friday," a senior US official told reporters as Kerry's team prepared to leave Paris for Moscow.
US officials expressed frustration that Assad is trying to set his own rules about which opponents he is prepared to talk to and which are irredeemable terrorists in his eyes.
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They insist Russia has committed to a political transition to end the war, and warn that if it can't get Assad to the table its own forces will get bogged down in the fighting.
Kerry is in near constant touch with his Russian opposite number, Foreign Minister Sergei Lavrov, but knows that the road to peace talks runs through the Kremlin.
"Obviously, he has a chance to meet with Lavrov all over the world," the senior US official said.
"President Putin is the decision-maker in Russia. It's important to have a chance to talk to him directly."
- 'Agree to disagree ' -
As a result Kerry will meet Lavrov at the foreign ministry then both will go to Putin's office to, in the words of Kremlin spokesman Dmitry Peskov, "inform him of their talks."
Ties have also been strained over the crisis in Ukraine, but the US side said it would not be drawn into bargaining with Russia over the sanctions it imposed over Moscow's interference there.
Russia, which has dispatched air and naval forces -- and some ground troops and advisors -- to protect Assad has agreed to help Washington pursue the peace plan.
But only after -- in talks last month in Vienna -- Kerry "agreed to disagree" with Moscow about Assad's fate. Moscow says it is for Syrian voters to tell him when to go.
The US believes Assad's brutal crackdown on opposition protesters triggered the civil war and drove recruits to the Islamic State group when it profited from the chaos.
And America's regional allies, led by Saudi Arabia, are even more emphatic in declaring that Assad must go, demanding he step down as soon as peace talks begin.
The opposition leaders met last week in Riyadh and began the process of deciding their negotiating team -- but also repeated their demand that Assad step down immediately.
Meanwhile, back in Washington, US President Barack Obama voiced fresh determination to destroy the Islamic State, vowing to kill the group's leaders and win back territory in the Middle East.
On the ground in Syria, a military source said government troops recaptured a military airport and town east of Damascus, more than three years after they were overrun by rebel groups.
The war began with anti-government demonstrations in March 2011 but evolved into a multi-front civil war that has killed more than 250,000 people and forced millions from their homes.