Satellite images taken by a US firm of a large Russian military convoy near Ukraine's capital, Kyiv, show it has "largely dispersed and redeployed".
The convoy was last seen near Antonov Airport, north-west of Kyiv, and its movement could signal a renewed push towards the city.
The firm that took the photos, Maxar Technologies, said parts of the convoy were in positions in surrounding towns.
Other parts are further north, with artillery now in firing positions.
The apparent redeployment came as Russian forces in Ukraine began attacking new targets in different areas of the country:
Sarah Rainsford, Eastern Europe correspondent, Dnipro
The air raid sirens went off at 04:30 and wailed for more than three hours. We now know the danger was real.
Officials here say there were three air strikes, hitting a small shoe factory, an apartment block and a kindergarten.
This city is full of heavy industry, including a rocket factory. There is a metalworks nearby the site that was hit, but no obvious military target.
Dnipro has been bracing for this since the war began. All the bridges and main roads here are heavily guarded. Residents have got used to scrambling to underground shelters when the sirens sound.
Even so, the city has been something of a safe haven, for people fleeing cities under sustained Russian attack. In the past few days, residents here had begun leaving: we saw giant queues for evacuation trains and the roads west out of town have been heavily congested. Now the city has been directly hit, I suspect more will be thinking of getting out.
"Ukrainian big cities are again subjected to devastating blows," said Ukrainian presidential adviser Mykhaylo Podolyak.
He added that the shelling in Lutsk had shut down two central heating compounds.
"Russia's destructive war against civilians and major cities continues," he said.
Russian state media reported that the Ukrainian city of Volnovakha had been captured by Russian-backed separatist forces.
There is no independent confirmation of the capture of the city, which is a northern gateway to the besieged port city of Mariupol.
President Volodymyr Zelensky has rejected Russian claims that chemical weapons or weapons of mass destruction were developed in Ukraine. In a video address, he also warned that Russia would get "the most severe sanctions response" if it were to use such weapons against Ukraine.
The US said earlier that Russia's claims of Ukraine hosting US-backed chemical weapons facilities was a "false flag", intended to justify Russia's possible use of such weapons.
Russia has requested an emergency meeting of the UN Security Council on Friday to discuss the alleged manufacture of biological weapons in Ukraine.
Russian forces moved three miles (5km) closer to Kyiv in the past 24 hours, a senior US defence official said on Thursday.
That meant Russian troops advancing from the north-west were now just nine miles from the city centre, the official - who spoke on condition of anonymity - told reporters.
Russian forces were also trying to close in on the city from the north-east, and were now about 25 miles (40km) away, the official said.
The northern city of Chernihiv was now "isolated" the official added.
The convoy was earlier seen stalled not far from the capital, where US officials said it was targeted by Ukrainian troops with anti-tank missiles. It is not clear how many of the vehicles currently seen on the move may have been an initial part of that first group.
Fierce battles have been raging in recent days in Irpin and Bucha, satellite towns just a few kilometres north-west of Kyiv. Thousands of civilians have been forced to flee their homes.
On Thursday, footage emerged apparently showing a Russian military column being hit by Ukrainian forces near the city of Brovary, just outside the capital.
Kyiv Mayor Vitali Klitschko says that half the population of the city of about three million has already fled, adding that Kyiv "has been transformed into a fortress".
"Every street, every building, every checkpoint has been fortified," the mayor said.
Tens of thousands of civilians have formed Territorial Defence units to help the Ukrainian armed forces defend the capital.