(CNN)Russia's invasion of Ukraine has been far costlier and less successful than most analysts expected over its first six weeks -- and experts now believe that Moscow is changing its military approach.
The fight for Sloviansk may be 'the next pivotal battle' of Russia's war in Ukraine
President Vladimir Putin's revised war strategy will now focus on trying to take control of the Donbas and other regions in eastern Ukraine with a target date of early May, according to several US officials familiar with the latest US intelligence assessments.
That makes the city of Sloviansk, more than 300 miles east of the capital Kyiv, a potentially crucial battleground in the coming weeks.
"Efforts by Russian forces advancing from Izyum to capture Slovyansk will likely prove to be the next pivotal battle of the war in Ukraine," the Washington DC-based think tank Institute for the Study of War (ISW) said in its Monday update on the conflict in Ukraine. Its report uses alternative transliterations of Ukrainian place names.
ISW expects Russian troops to begin offensive operations towards the city from nearby Izium in the coming days, a forecast that matches warnings on the ground.
"They go south to Kamyanka because it is the road to the city of Sloviansk," Max Strelnyk, a deputy in the Izium city council's office, told CNN late last week of Russian troops' plans. "We have radio interceptions of their talks; their task is to capture the Donetsk region from the north."
On Wednesday, Vadym Denysenko, adviser to Ukraine's Ministry of Interior, said: "If we talk about the key directions where combat will be ongoing -- it's the Sloviansk [Donetsk region] and Barvinkove [Kharkiv region] directions."
Residents of Sloviansk, a city of just over 100,000 people before the invasion, are now being urged to evacuate, while Ukrainian forces are preparing to defend it from a new Russian onslaught.
Control of the city has significant strategic importance in the wider conflict. Should Russian forces overrun Sloviansk, they would be able to cut off Ukraine's forces in the wider region. If they are held back by Ukrainian resistance, however, Russia's ambitions to control both the Luhansk and Donetsk regions will suffer a huge blow.
Sloviansk was a major flashpoint in the war in the Donbas region in 2014, and was briefly held by pro-Russian separatists before they were pushed back by Ukrainian forces in July of that year.
Its significance now lies primarily in the fact that it is surrounded on three sides by Russian-held cities -- Izium to the north, Luhansk to the east, and Donetsk to the south -- but lies deeper west in the Donbas region than the two latter locations, blocking Russia's pathways further into Ukrainian territory.
"Russian forces likely intend to cut off Ukrainian forces in eastern Ukraine and will need to take Slovyansk as their minimum step to do so," the ISW said.
A successful Russian assault on the city would give Moscow the option to link troops up with those fighting in Rubizhne, to the northeast of Sloviansk, or move them south, towards Horlivka and Donetsk, in an attempt to encircle Ukrainian fighters there, the group added.
But Russia appears to have encountered multiple military failures during the first six weeks of the invasion, and its inability to capture cities further west, such as the capital Kyiv, has likely prompted its renewed focus on the Donbas.
In that context, a fresh Russian defeat in the face of Ukrainian resistance could imperil even their new strategy in the east.
"If Russian forces are unable to take Slovyansk at all, Russian frontal assaults in Donbas are unlikely to independently breakthrough Ukrainian defenses and Russia's campaign to capture the entirety of Luhansk and Donetsk oblasts will likely fail," the ISW said.