For two superpowers with frosty relations, the United States and Russia have seemed not as chilly or isolated from each other recently. U.S. Secretary of State John Kerry has just wrapped up his third trip to the Russian capital in a year.

His mission in Moscow centred on Syria, but Kerry also ushered in a warm front, interpreted as a softening of the often-hostile rhetoric between the U.S. and Russia.

On the surface, it seems to have worked. President Vladimir Putin was unusually complimentary of the U.S. role in the Syrian peace initiative.

The groundwork we have on Syria could only have been possible thanks to the supreme political leadership of the United States. - Vladimir Putin

"We are aware that the groundwork we have on Syria could only have been possible thanks to the supreme political leadership of the United State, specifically the position of President Obama," the Russian president said at the start of a four-hour meeting with Kerry.

And the secretary of state left Russia Friday morning with an agreement to speed up the timetable, aiming for a new Syrian draft constitution by August.

Washington asked for this latest meeting after Putin suddenly drew down the bulk of Russian troops in Syria.

U.S. Secretary of State John Kerry meets his counterpart Sergei Lavrov in Moscow. There were more media representatives at the photo op than any previous meeting between the two in Russia. (Susan Ormiston/CBC )

Kerry opened his day-long meetings Thursday teasing his counterpart Sergei Lavrov about his recent birthday.

"I'd like to take this opportunity to wish you Happy Birthday," said Kerry. "I know it will give you wisdom in our talks today."

Not to be outdone, Lavrov quipped back, "If wisdom is measured in birthdays, John, I'm still behind you."

These two veterans of diplomatic wars hoped to make progress on a political path for peace in Syria.

Russian Foreign Minister Sergei Lavrov reviews notes for a significant meeting with U.S. Secretary of State John Kerry in Moscow on Thursday. (Corinne Seminoff/CBC)

In an unguarded moment off camera, Kerry acknowledged to an aide: "A lot is riding on this meeting."

The Kremlin has positioned itself so that any road to peace in Damascus must pass through Moscow. Washington knows it will need Putin's influence to help with the thorniest question of the peace talks — what happens to Syrian President Bashar al Assad.

Late Thursday night, Kerry emerged with conciliatory words.

"All of us are going to try to get President Assad to make the right decision in these next days, to engage in a political process that results in a genuine transition and in peace for Syria," said Kerry, acknowledging Russia's critical role, while not revealiing what its position is on Assad. All of us are going to try to get President Assad to make the right decision in these next days. - John Kerry "I believe Russia is fully engaged in this effort," Kerry said. Syrian government representatives at this month's Geneva peace talks have demanded Assad cannot be negotiated out of office. Contrarily the opposition won't continue with the talks unless Assad removes himself as part of a transitional government.

U.S.- Russia relations hit a new low two years ago, after Russian annexed Crimea and supported separatist rebels in eastern Ukraine. International sanctions followed, isolating Russia.

But the urgency of the Syrian crisis has pulled the two countries towards each other like a huge geopolitical magnet; a recognition that co-operation might be the only route left for a solution to Syria.

"Layer upon layer, [Kerry] tries to re-establish a strong basis for Russian-American relations," says Viktor Kremeniuk, deputy director of the Institute of USA and Canada in Moscow.

John Kerry, left, has made three shuttle diplomacy trips to Russia in the last year. (Susan Ormiston/CBC)

Kerry's visit and his close working relationship with Lavrov are positioning the U.S. for the near future, he says.

"We are working today, not on what will happen within a month, not what will happen before the summer, but what will happen when the new American president is elected," says Kremeniuk. "And he thinks his professional task is to prepare for this period."

But there remain sharp shoals. Détente in Ukraine a major one. Kerry and Lavrov said they would each re-engage pressure on Kyiv and eastern Ukraine to stick to obligations agreed to in the Minsk accord last year.