A senior White House official has voiced cautious optimism that the United States and Russia could reach an agreement on a political transition in Syria, which Washington says will be a focus of talks in Moscow next week between U.S. Secretary of State John Kerry and Russian President Vladimir Putin.

Celeste Wallander, senior director for Russia and Central Asia on U.S. President Barack Obama’s National Security Council, said "it’s clear” that an agreement is possible between the U.S.-led coalition and Moscow on the political exit of Syrian President Bashar al-Assad, Russia's staunch ally, as part of a transition in Syria.

“We wouldn’t be having these negotiations if we didn’t think that there was a possibility that Russia's position is evolving such that we could agree,” Wallander told RFE/RL in a December 11 interview.

The United States and its allies have insisted that Assad cannot be part of any peaceful resolution to the nearly five-year-old civil war in Syria, where his forces are fighting both Islamic State (IS) militants and moderate opposition groups -- some backed by the U.S.-led coalition -- seeking to oust him.

Russia rejects that position, saying it should be up to the Syrian people to choose their leader and that Assad’s army is the force most capable of defeating IS fighters that have captured large swaths of Syria and Iraq.

"I don’t know that the positions have come closer, but it's clear that there could be an agreement on a transition that meets U.S. and coalition requirements that Assad not be part of Syria’s leadership, and those are the discussions that are under intensive focus right now,” Wallander said.

The State Department announced earlier in the day that Kerry will visit Moscow on December 15 to meet with Putin and Russian Foreign Minister Sergei Lavrov.

“They will discuss ongoing efforts to achieve a political transition in Syria and related efforts to degrade and destroy ISIL,” the State Department said in a statement, using an alternate acronym for the extremist group.

Russia in late September began bombing armed groups fighting Assad in what Moscow has framed as a counterterrorist campaign. The United States and its allies have accused Moscow of bombing the moderate Syrian opposition and using its military intervention to prop up Assad rather than targeting IS positions -- criticism that Russia has rejected.

Wallander said the "political process that's underway" in Syria would be the primary focus of Kerry's visit to Moscow, which comes ahead of planned talks in Vienna next month between Syrian opposition groups and the government on a political solution to the conflict.

But she said they would also look at how Russia can "match its rhetoric to its actual actions and to get serious about fighting ISIL, not about defending [Assad’s] regime.”

"The overwhelming majority of Russian military actions and support is to the Assad regime, to the Assad military forces," Wallander said.

She added, however, that since the downing of a Russian passenger plane over Egypt in October that killed all 224 people on board, which IS militants claimed responsibility for, Russian bombers have struck IS targets "with somewhat more frequency."

The State Department said Kerry will also discuss the Ukraine conflict and "stress the need for full implementation" of the Minsk accords to halt violence between Kyiv's forces and Russian-backed separatists in eastern Ukraine that the UN says has killed more than 9,000 people since April 2014.

U.S. Vice President Joe Biden told Ukraine’s parliament this week that Washington "will maintain pressure until Moscow fulfills its Minsk commitments" and that that U.S. sanctions against Moscow will remain in place "until Russia meets all of its commitments under the” accords signed in February.

Kremlin spokesman Dmitry Peskov responded ambiguously to a question about whether a Putin-Kerry meeting would take place.

"If you ask me whether the meeting [of Kerry] with Putin will take place, I will repeat once again that we do not rule out the possibility of such a meeting," the state-run TASS news agency cited Peskov as saying on December 11.