Russia has been forced to merge and redeploy depleted and disparate units from failed advances in northeast Ukraine, a British military update said on Saturday.
"Shortcomings in Russian tactical coordination remain. A lack of unit-level skills and inconsistent air support have left Russia unable to fully leverage its combat mass, despite localised improvements," the military tweeted.
"Russia hopes to rectify issues that have previously constrained its invasion by geographically concentrating combat power, shortening supply lines and simplifying command and control," it said.
Russian forces pounded Ukraine's eastern Donbas region on Saturday but failed to capture three target areas, Ukraine's military said.
It came as Moscow said Western sanctions on Russia and arms shipments to Ukraine were impeding peace negotiations.
The Russians were trying to capture the areas of Lyman in Donetsk and Sievierodonetsk and Popasna in Luhansk, the General Staff of Ukraine's Armed Forces said in a daily update.
"Not succeeding - the fighting continues," it said.
Russian Foreign Minister Sergei Lavrov, in remarks published early on Saturday, said lifting Western sanctions on Russia was part of the peace talks, which he said were difficult but continued daily by video link.
Ukrainian President Volodymyr Zelenskiy has insisted since the Russian invasion began on February 24 that sanctions needed to be strengthened and could not be part of negotiations.
He said on Friday there was a high risk the talks would end because of what he called Russia's "playbook on murdering people".
Thousands of military personnel continue to rehearse with ballistic missile launchers and tanks for this year’s Victory Day parade in Russia when Vladimir Putin may declare war on the West.
Each year Russia celebrates its triumph over Nazi Germany in 1945 at the end of the Second World War on May 9, and this year it has extra significance.
Putin’s forces invaded Ukraine on February 24 in what he called a “special operation to de-Nazify” the country and it was widely expected that he wanted to use this year’s celebrations in May to announce a success in that mission.
But with Russia having faced stiff resistance from Ukrainians the invasion has not gone to plan and they have been forced to concentrate their attacks on the east of Ukraine having failed to topple Kyiv.
This year considerable effort has been put into the victory parade with regular rehearsals using heavy military being taken through the streets of Moscow and St Petersburg in an intended show of strength.
