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On 17 March, Russian President Vladimir Putin held a ceremony for troops returning from Syria and commemorated the six servicemen who lost their lives during the six-months overseas deployment.

Officially, Moscow also made it clear it is not closing the book on Syria but instead starting a new chapter in its existential conflict.

Russia still controls Latakia airbase and Tartous port which would make a redeployment of troops relatively quick and simple.

Then on Monday, the foreign ministry issued a stark warning to rebel forces about a possible return of Russian troops.

"We do not rule out the possibility that we will have to unilaterally use force to curb the actions of the rebels who fail to comply with the ceasefire arrangements."

Partial withdrawal

During Russia's six-months blitz of Syria, the rebels were the primary targets of Russian bombing. Few analysts were convinced by Moscow's claims it was concentrating attacks on the Islamic State group or other "terrorist groups".

Now that the Syrian regime is engaged in an offensive against IS in Palmya - and battlelines with rebels remaining static - Russian military planners seem unconcerned with the war.

"Russian ministry of defence officials have claimed they carried out between 20 and 25 sorties against IS in Palmyra, but we've yet to see any solid proof of Russian airstrikes continuing against IS or any other targets," said Ruslan Leviev, head of .

According to Leviev's estimates, Moscow left behind around ten Su-24 Fencer bombers in Syria, which could easily be deployed in the battle against IS militants around the ancient city.

What is significant about the Su-24s and other hardware left behind by the Russians - such as Mi-24 and Mi-8 helicoptors - is that the aircraft also appear to be in the regime's arsenal.

"They are the only [aircraft] also operated by the regime, which makes it suspicious that they were the only ones left in Syria after the 'hybrid withdrawal' from Syria," said Leviev. 

"This highlights that any further Russian actions in Syria could be easily attributed to the regime due to them having the same attack hardware."

Redeployed

This would blur the lines between regime and Russian air raids, particularly if civilians are killed or moderate rebel groups targeted.

This is particularly important after the Russian air force came under attack by human rights groups for bombing hospitals, homes and school, despite Moscow's unconvincing denials.

"We believe the Su-24s could have been left there in order to be able to shift the blame for any further airstrikes on civilians on the regime."

There is scant proof that any of these aircraft have been engaged against jihadi forces not part of the ceasefire, despite widespread but unverified reports of Russia bombing against IS.

"We cannot know either way, we need more solid evidence like videos on the ground. There are subtle but spottable differences between Syrian Air Force and Russian Air Force Su-24s filmed from the ground," said Leviev.

However, judging from what evidence he has Leviev and the investigative team remain unconvinced that Russia has engaged with IS since the ceasefire. In fact, they believe that most pilots returned home.

However, Ka-52 and Mi-28N attack helicopters were transferred to Syria during the pull-out of Russian strike aircraft. This hightens concerns that Russia's war against the rebels is not yet over, and the ceasefire could face difficulties.