Russian forces are firing at a nuclear research facility in the city of Kharkiv, the Ukrainian parliament said in a Twitter post on Saturday.
"It is currently impossible to estimate the extent of damage due to hostilities that do not stop in the area of the nuclear installation," the post quoted the State Nuclear Regulatory Inspectorate as saying.
Earlier this month the grounds of the Institute of Physics and Technology were hit by Russian shells. At the time, the facility's director-general said the core housing nuclear fuel remained intact.
Earlier, The mayor of Lviv said another rocket had hit the city in western Ukraine on Saturday, not long after two rockets struck its outskirts in what appeared to be the first attacks within the city's limits since the start of the war with Russia.
This signaling a potential new front in Moscow's invasion as U.S. President Joe Biden decried Russian President Vladimir Putin's grip on power and sought to steel Europe for a long fight ahead.
Lviv, some 60 kilometers (40 miles) from the Polish border, has so far escaped the bombardment and fighting that has devastated some Ukrainian cities closer to Russia since Moscow launched its invasion on Feb. 24.
On Saturday Governor Maksym Kozytskyy said two rockets had struck the city's eastern outskirts in the mid-afternoon and ordered residents to take shelter.
Later, Mayor Andriy Sadoviy said there had been another strike. "One more rocket strike on Lviv," he said in an online post.
He did not share details of the location. He said the strike had damaged infrastructure but not residential buildings.
The first strikes set fire to an industrial facility storing fuel, but had not hit residential areas, Sadoviy said earlier.
Governor Kozytskyy said five people had been wounded in that attack, citing preliminary figures.
"Stay in shelters! Do not go out into the streets!," he warned.
Russian forces have taken control of Ukraine's Slavutych, where workers at the defunct Chernobyl nuclear plant live, the governor of the Kyiv region said on Saturday.
In an online post, Governor Oleksandr Pavlyuk did not describe how the town had been taken but said some residents had unfurled a large Ukrainian flag and shouted "Glory to Ukraine" in protest.
He also said the Russians fired into the air to disperse the pro-Ukraine protest in the center of the town and had thrown stun grenades into the crowd.
There was no immediate comment from Russia about Slavutych.
Slavutych sits just outside a safety exclusion zone around Chernobyl - the site of the world's worst nuclear disaster in 1986 - where Ukrainian staff has continued to work even after the territory was occupied by Russian forces soon after the start of the Feb. 24 invasion.
Presidential adviser Oleksiy Arestovych said the town had become a new hotspot of the war. "The inhabitants are carrying out heroic civil resistance to the invader," he said in a televised address, referring to Saturday's protest.
On Friday, Ukraine said Russian troops had drawn close to the town, which had a pre-war population of around 25,000, and had launched an unsuccessful first attack.
Since then, "the Russian occupiers have invaded the town of Slavutych and seized the city hospital," Governor Pavlyuk said.
In an online post, the city council asked residents, to remain calm. "The occupiers' vehicles are moving around the city to check for weapons. Please do not provoke (them) or endanger yourselves."
Russian military drills
Russia has staged military drills engaging S-400 surface-to-air missiles in its western Kaliningrad exclave, Interfax reported on Saturday, citing the Baltic Fleet.
It said that Su-27 fighter jets were also deployed in the exercises.
Russia was conducting drills on islands claimed by Tokyo, Japanese media said on Saturday, days after Moscow halted peace talks with Japan because of its sanctions over Russia's invasion of Ukraine.
Russia's Eastern Military District said it was conducting military drills on the Kuril islands with more than 3,000 troops and hundreds of pieces of army equipment, Russia's Interfax news agency said Friday.
It did not say where on the island chain, connecting Russia's Kamchatka peninsula and Japan's northernmost main island of Hokkaido, the drills were taking place. Japanese media said they were on territory the Soviet Union seized at the end of World War Two that is claimed by Tokyo.
Japan's Foreign Ministry and Prime Minister's Office could not be reached outside business hours to comment on the exercises.
The territorial dispute over the four islets - which Russia says are part of its Kuril chain and which Japan calls its Northern Territories - has prevented Tokyo and Moscow from reaching a peace treaty formally ending hostilities.
Japan reacted angrily on Tuesday after Russia withdrew from long-running treaty talks and froze joint economic projects related to the islands, in retaliation for Japan joining Western sanctions over Moscow's month-old invasion.
Russia's exercises involved repelling amphibious warfare, including destroying defense aircraft carrying troops and testing skills to operate fire control systems of anti-tank guided missiles, Interfax said.
"In addition to this, units of the Air Defense Forces are carrying out a set of measures to detect, identify and destroy aircraft of a mock enemy that would carry out an airborne assault," the agency cited the District's press service as saying.
Laid waste
Footage from Mariupol, home to hundred of thousands of people before the war, showed destroyed buildings, burnt vehicles and shell-shocked survivors venturing out for provisions. Residents have buried victims in makeshift graves as the ground thaws.
"It's scary, I don't know how we're going to survive," an elderly woman resident said, declining to identify herself by name. "We're lying there, hoping they won't bomb us. Look at how many dead bodies we've buried around the building."
Evacuation efforts
A total of 5,208 people were evacuated from Ukrainian cities through humanitarian corridors on Saturday, a senior official said, fewer than the 7,331 who managed to escape the previous day.
Kyrylo Tymoshenko, deputy head of the president's office, said in an online post that 4,331 people had left the besieged city of Mariupol.