Russian forces appear to have made progress from northeast Ukraine in their slow fight to reach the capital Kyiv.
Their tanks and artillery have bombarded areas with such heavy shelling it stopped residents of one city from burying an increasing number of dead.
Relentless barrages in Mariupol have thwarted repeated attempts to bring in food and water and evacuate trapped civilians.
The Russian military had shelled a mosque there sheltering more than 80 people, according to the Ukrainian government. No casualties were reported.
Ukraine's military said Russian forces have captured the eastern outskirts of Mariupol, but added that Russian Major General Andrei Kolesnikov had died in the fighting.
The Mariupol mayor's office said the city's death toll has surpassed 1,500 in 12 days. A bombardment of its maternity hospital killed three people.
Continued shelling forced crews to stop digging trenches for mass graves, so the "dead aren't even being buried", the mayor said.
More than a dozen hospitals have been hit by the Russians, according to the World Health Organisation.
The invaders have struggled more than many expected against determined Ukrainian resistance. However, Moscow's stronger military threatens to grind down the defence.
Two-and-a-half million Ukrainians have fled their homeland. It is believed thousands of soldiers on both sides have been killed, along with many Ukrainian civilians.
The Kremlin's forces appeared to be trying to regroup and regain momentum.
They were blockading Kharkiv – Ukraine's second-largest city – despite efforts to create new humanitarian corridors around it to evacuate residents.
The Russians also stepped up attacks on Mykolaiv, 290 miles south of Kyiv, in an attempt to encircle the city.
Watch: Rare access as crews patrol NATO's frontline amid Ukraine conflict.
In a multi-front attack on the capital, the Russians' push from the northeast appeared to be advancing, a US official said. Combat units were moved up from the rear as the forces advanced to within 20 miles of Kyiv.
The UK's Ministry of Defence said fighting northwest of Kyiv has continued with the bulk of Russian ground forces now about 15 miles from the centre of the city.
A daily intelligence update said elements of the large Russian military column north of Kyiv have dispersed. It said this is likely to support a Russian attempt to encircle the capital and could also be an attempt by Russia to reduce its vulnerability to Ukrainian counter attacks, which have taken a significant toll on Russian forces.
New satellite images appear to show artillery firing on residential areas that stand between the Russians and Kyiv. Maxar Technologies, which supplied the images, said they showed muzzle flashes and smoke from big guns, impact craters and burning homes in Moschun – a town 20 miles from the capital.
In the economic and political responses, the US and its allies moved to further isolate and sanction the Kremlin. President Joe Biden announced the US will dramatically downgrade its trade status with Russia and ban imports of Russian seafood, alcohol and diamonds.
Russian President Vladimir Putin said there had been "certain positive developments" in Russia-Ukraine talks but gave no details.
Ukrainian President Volodymyr Zelensky appeared on video to encourage his people to keep fighting.
Watch: What does the 'Z' on Russian military vehicles mean?
According to US defence officials, Russian jets are averaging 200 sorties a day, compared to five to 10 for Ukrainian forces, who are focusing more on surface-to-air missiles, rocket-propelled grenades and drones to take out Russian aircraft.
The US also said Russia has launched nearly 810 missiles into Ukraine.
US soldiers have continued to deploy to Europe, joining thousands already sent overseas to support NATO allies amid Russia's invasion.
About 130 soldiers from the 87th Division Sustainment Support Battalion, 3rd Division Sustainment Brigade gathered Friday at Hunter Airfield in Savannah, Georgia and departed on a chartered flight.
The soldiers are in addition to the estimated 3,800 soldiers from the US Army's 3rd Infantry Division who deployed recently from nearby Fort Stewart.
Until recently, Russia's troops had made their biggest advances on cities in the east and south while struggling in the north and around Kyiv. They also have started targeting areas in western Ukraine, where large numbers of refugees have fled.
Russia said on Friday that it had used high-precision long-range weapons to put military airfields in the western cities of Lutsk and Ivano-Frankivsk "out of action". The attack on Lutsk killed four Ukrainian servicemen, the mayor said.
Russian air strikes also for the first time targeted Dnipro, a major industrial hub in the east and Ukraine's fourth-largest city, with about a million people. One person was killed, Ukrainian officials said.
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