Sumy oblast governer, Dmytro Zhyvytskyy, issued a warning on Tuesday that Russian armor is moving through the village of Nizy and its surrounding area, donning white flags and shooting openly at civilians.
The governor has instructed citizens to stay indoors and stay away from windows.
Russia's advance on Kyiv has made little progress in the past 24 hours due to logistical difficulties. The Russian army has increased its use of artillery north of the capital, a British military intelligence update said.
"The Russian advance on Kyiv has made little progress over the past 24 hours, probably as a result of continuing logistical difficulties," the British defense ministry said in a military intelligence update.
"Russian forces have increased their use of artillery north of Kyiv and in [the] vicinities of Kharkiv and Chernihiv. The use of heavy artillery in densely populated urban areas greatly increases the risk of civilian casualties."
"Russia has failed to gain control of the airspace over Ukraine, prompting a shift to night operations in an attempt to reduce their losses," it said.
Reuters was unable to immediately verify the information.
Satellite images taken on Monday show a Russian military convoy north of the Ukrainian capital of Kyiv that stretches for about 40 miles (64 km), substantially longer than the 17 miles (27 km) reported earlier in the day, a private US company said.
Maxar Technologies MAXR.N also said deployment of additional ground forces and ground attack helicopter units were seen in southern Belarus, less than 20 miles (32 km.) north of the Ukrainian border.
Air sirens have also been heard in Kyiv, Vinnytsia and Bila Tserkva, as well as in Volyn, Ternopil, and Rivne oblasts (administrative divisions) early Tuesday morning, according to the Kyiv Independent.
Russian troops based in the country's far east will hold drills in the Astrakhan province which lies on the border between the European and Asian parts of Russia, the Interfax news agency quoted Russia's eastern military district as saying on Tuesday.
The troops will train in long-distance movements of military units, among other tasks, the district command said.
A Russian-backed separatist leader in eastern Ukraine said his forces aimed to encircle the Ukrainian port of Mariupol on Tuesday, RIA news agency said.
"The task for today is to directly encircle Mariupol," it quoted Donetsk separatist leader Denis Pushilin as saying in a television interview.
In addition, Ukraine has cut connections for Russian cellphone numbers in the country, according to the Derzhspetszviazok – the State Service of Special Communications and Information Protection of Ukraine, which is the country's intelligence and technical security service.
In response to this, however, Russian forces are reportedly seizing phones from Ukrainian citizens, according to the Derzhspetszviazok, who call on those whose phones were stolen to call their operators to block their numbers.
This is despite the fact that they would need a phone to call the phone company in the first place, but the agency recognizes this difficulty.
"We understand that doing this when your phone has been stolen isn't easy," the service said. "However, this is very important. Find neighbors who have a phone, use a landline. The security of our state and the lives of Ukrainians depend on it."
In addition, Ukraine will allow foreigners traveling to the country to help fight against Russia to do so without a visa, according to a new decree signed by the president that went into effect Tuesday.
The decree, signed by President Volodymyr Zelensky, allows for all foreigners hoping to join the new unit for foreign volunteers, known as the International Legion of the Territorial Defense Force, with the exception of those coming from Russia.
The new unit for foreign volunteers was announced on Sunday, with Ukrainian authorities having said the next day that thousands have already applied to join.
Some young volunteers are traveling straight to Ukraine to enlist.
Others are applying at Ukrainian embassies and consulates before quitting jobs or dropping out of university.
A Texas software developer and a cook in British Columbia are among dozens of Americans and Canadians answering Ukraine's call.
"I feel guilty to not go," said Dax, 26, a veteran of the elite US 82nd Airborne Division infantry, who planned to deploy with other former US military personnel. Like many volunteers, the Alabama native declined to give his full name amid discussion on social media of the need to keep their identities and movements secret for security reasons.
Canadian Bryson Woolsey quit his job as a cook on Sunday after seeing Zelensky's appeal. He has no military training and plans to buy a plane ticket to Poland, cross into Ukraine and volunteer for combat.
"I felt like I had to do something," said the 33 year old from Powell River, British Columbia, who became restless as he watched images of wounded women and children in Ukraine.
Canada's Foreign Minister Melanie Joly told reporters on Sunday that it was up to individual Canadians to decide whether they wanted to join Ukraine's international brigade. The US State Department did not immediately respond to a request for comment.
In Austin, Texas, a software developer said he would draw on his experience as a US Army cadet to fight for Ukraine.
"If they're willing to defend democracy then I think those that benefit from a democratic society are duty-bound to support them," said the 25-year-old, who asked that his name not be used. "I'm not telling my parents until I head to the airport."
Not all volunteers want to fight, however.
In Quebec, 35-year-old physician Julien Auger was preparing to leave his young family to become a medic with Ukraine's health ministry and provide "neutral" humanitarian aid.
"Global opinion and support is the key right now to solving the conflict," said Auger, a father of two who provides palliative care at a hospital in Saint-Jérôme.
The ongoing fight
The fighting in Ukraine has been fierce with reports of numerous Russian heavy bombardments throughout the country.
According to Zelensky, Russia has reportedly carried out 56 rocket strikes and sent 113 cruise missiles into Ukraine since the invasion began.
Russian forces have also reportedly heavily shelled the city of Kharkiv, which Zelensky has said is being a war crime.
According to Ukrainian Ambassador to the US Oksana Markarova, Russian forces used an illegal weapon known as a vacuum bomb against Ukraine.
A vacuum bomb uses oxygen from the surrounding air to generate a high-temperature explosion, typically producing a blast wave of a significantly longer duration than that of a conventional explosive.
Though the fighting has been fierce and Russian forces are still advancing, the General Staff of Ukraine's Armed Forces said that it is unlikely that Russian troops will attempt a naval landing in the coming days, according to the Ukrainian news outlet New Voice of Ukraine.
Belarus has no plans to join Russia's military operation in Ukraine, President Alexander Lukashenko was quoted as saying on Tuesday.
Lukashenko denied Kyiv's allegations that Russian troops were attacking Ukraine from Belarus' territory, Belarusian state news agency Belta reported.
This is a developing story.