U.S. Secretary of State John  Kerry arrived in Moscow on Wednesday seeking answers from President Vladimir Putin on how Russia views a political transition unfolding in Syria, in particular the fate of President Bashar al-Assad.

Now that a fragile truce in Syria is in place and warring sides have begun peace talks in Geneva, Kerry wants to "get down to brass tacks" on the question of Assad, a U.S. State Department official said before the meeting at the Kremlin on Thursday.

The meeting was arranged after Putin's surprise announcement on March 14 that he was partially withdrawing Russian forces from Syria.

The attacks in Brussels on Tuesday further underscored the need to tackle the threat posed by ISIS militants, the official said.

John Kerry-Moscow

U.S. Secretary of State John Kerry arrived in Moscow Wednesday and will be meeting with Russian President Vladimir Putin and Defence Minister Sergei Lavrov to discuss the issue of how Syria can transition from civil war to political stability. (Maxim Zmeyev/Reuters)

"The secretary would like to now really hear where President Putin is in his thinking ... on a political transition in [Syria]," said the official, speaking on condition of anonymity.

"They have had quite a bit of contact with Assad in recent weeks, and, obviously, if the cessation of hostilities is 
going to transform into a true transition for Syria, it is going to have to involve getting down to brass tacks on what that 
political transition looks like."

Russia has repeatedly said that only the Syrian people can decide Assad's fate at the ballot box and has bristled at any talk of regime change.

Peace talks will be long and difficult

Kremlin spokesman Dmitry Peskov said on Wednesday that peace negotiations on the Syria conflict taking place in Geneva were always set to be long and difficult, and that it was too early to talk about patience running out on any side of the negotiations.

After five years of a conflict that has killed over 250,000 people and caused the world's worst refugee crisis, Washington and Moscow engineered a deal three weeks ago for a cessation of hostilities and crucial humanitarian aid to besieged areas.

The State Department official said the meetings with Putin and Foreign Minister Sergei Lavrov would evaluate the status of the ceasefire "which was going better than a lot of people expected, albeit with significant violations every day."

The statesmen will also try to "get on the same page" about ending violations and increasing humanitarian assistance, the official said. Russia this week threatened to act unilaterally against those who violate the Syrian ceasefire unless the United States and Moscow reached a deal on measures for detecting and preventing truce breaches.

The Syrian opposition has accused government forces of renewing sieges and stepping up a campaign of barrel-bombing across the country.

Vladimir Putin

Putin announced on March 14 that he was partially withdrawing Russian forces from Syria, where Russia had been conducting airstrikes since last fall. He has insisted that only the Syrian people can decide whether or not Bashar al-Assad should remain in power. (Kirill Kudryavtsev/Reuters)

In Geneva, where warring sides are a week into talks on ending the conflict, government officials have rejected any 
discussion on the fate of Assad, who opposition leaders say must go as part of any transition.

UN special envoy on Syria Staffan de Mistura said on Tuesday he hoped the U.S.-Russia meeting would give an impetus to the peace talks where the divisive issue of a political transition is stalling progress.

But the State Department official played down expectations that the meeting would have an immediate impact on the peace talks, saying: "I would not be looking for a big headline in that regard."

"Obviously, what we are looking for, and what we have been looking for, is how we are going to transition Syria away from Assad's leadership," the official said.

Ukraine also on agenda

Kerry will also use the Kremlin meeting to raise concerns over a Russian court decision on Tuesday to jail Ukrainian pilot Nadezhda Savchenko for 22 years.

The U.S. has said the sentence showed a "blatant disregard for the principles of justice" and contravened Russia's 
commitment to the Minsk peace accords in Ukraine.

USA-CUBA/

Kerry's visit to Russia comes on the heels of U.S. President Barack Obama's historic trip to Cuba, which Kerry also attended. He'll go on to Belgium on Friday to meet with Belgian and European officials about the Brussels attacks. (Carlos Barria/Reuters)

The State Department official said Kerry would also discuss the implementation of the Minsk peace accords and concerns over an increase in violations of the deal.

"Of particular concern to us is the sharp increase in violations of the ceasefire and firing on the contact line that 
we have seen since the new year but which have accelerated quite a bit in the last few weeks," the official said.

"Unless and until we can get true quiet on the line and get full OSCE access, it is going to be hard to move onto other aspects of Minsk."