UK officials say most Russian forces are about 18 miles or 30 km from Kiev's center, according to The Guardian.
On Saturday morning, the Ministry of Defence published an intelligence update saying that Russia did not yet control airspace over Ukraine, thereby reducing its effectiveness.
"Russian casualties are likely to be heavy and greater than anticipated or acknowledged by the Kremlin," it added.
James Heappey, UK armed forces minister, has denied Russian claims that it has taken Melitopol. He claims the invasion plan is running "nowhere near" schedule, The Guardian reported.
The UK government armed forces junior minister said Russia has failed to achieve its initial objectives -- and fighting outside Kiev was limited to Russian special forces units, the report reads.
James Heappey spoke to BBC Radio 4's Today program about the failure of Russian attempts to take key Ukrainian cities. He said the UK did not believe the Russian claims that the south-east city of Melitopol was under their control.
The Guardian reported that"The Ukrainian resistance to the Russian advance appears extraordinary. All of Russia's Day One objectives of Kharkiv, Kherson, Mariupol, Sumy and even Melitopol, which the Russians are claiming to taken but we can't see anything on that, are still all in Ukrainian hands."
"The fighting on the outskirts of Kiev overnight, we understand to just be Russian spetsnaz special forces and pockets of paratroopers. The reality is the armoured columns coming down from Belarus and the north to encircle Kiev are still way off, because they have been held off by this incredible Ukrainian resistance," the report read.