According to Ukrinform, the UK Ministry of Defense said this in its latest intelligence update published on Twitter.
According to the update, Russian shelling and strikes on the Donbas line of control continue to grow, with the Ukrainians repelling numerous attempted advances by Russian forces.
"Russia's ability to progress continues to be impacted by the environmental, logistical and technical challenges that have beset them so far, combined with the resilience of the highly-motivated Ukrainian armed forces," British intelligence said.
According to the report, Russia's inability to stamp out resistance in Mariupol and their indiscriminate attacks, which have harmed the resident civilian populace, are indicative of their continued failure to achieve their aims as quickly as they would like.
The General Staff of the Armed Forces of Ukraine reported earlier that as of 06:00 on April 20, Russian troops are regrouping in order to continue their offensive toward the town of Lyman in the Donetsk region. The invaders are concentrating their main efforts on the capture of Mariupol, continuing to assault the area of the Azovstal plant.