The city of Avdiivka saw some of the most intense shelling since violence escalated in Ukraine earlier this week
. Avdiika is under Ukrainian government control in the separatist Donetsk region.
At least 18 Ukrainian soldiers were injured, said the spokesman, Col. Oleksandr Motuzyanyk. Two civilians, including a foreign photojournalist, also were hurt, he said.
Fighting between Russian-backed rebels from the self-proclaimed Donetsk People's Republic and the Ukrainian army exploded Sunday. Russia accuses Ukraine of starting the escalation.
After pro-Russian President Viktor Yanukovych's ouster in February 2014, Russian troops poured into the Crimean Peninsula. Russia annexed Crimea, an autonomous region of southern Ukraine, the following month.
In the last 24 hours, Ukraine recorded the most intense firing by pro-Russian rebels on its positions in eastern Ukraine in a year, said Oleksandr Turchynov, secretary of Ukraine's National Security and Defense Council, in a statement Friday.
About 200 people have been evacuated from Avdiivka, nearly half of them children, Ukraine's State Emergency Service said Friday. Some 8,000 people have turned out to receive help as temperatures remain below freezing.
Intense shelling was also reported overnight in the separatist-held city of Donetsk.
Vitaly Zarubin, a Donetsk People's Republic spokesman, said two civilians were killed and nine wounded in the shelling.
Eighteen fighters have been killed and 26 wounded since this week's uptick in violence, separatist military spokesman Eduard Basurin said Friday. Six civilians have been killed and 34 injured, he said, calling the situation "extremely tense.
The Ukrainian military didn't report casualties in Donetsk.
Ukrainian President Petro Poroshenko denounced the violence in Avdiivka.
"Nobody has a right to indifference when a traditional Russian scenario of taking the whole town hostage is being implemented right in front of our eyes," Poroshenko said in a statement Thursday.
"Moscow puts Avdiivka on the brink of humanitarian disaster -- cruelly and ruthlessly."
Ukrainian intelligence has seen an increase in military equipment, ammunition and weapons coming from Russia through uncontrolled border areas, according to Turchynov of Ukraine's National Security and Defense Council.
Russian Foreign Ministry spokeswoman Maria Zakharova on Friday blamed the Ukrainian government for the violence and called the situation in eastern Ukraine "the shame of modern Europe."
On Thursday, Nikki Haley, the new US ambassador to the United Nations, offered a strong condemnation of Russia at the UN Security Council, calling on Moscow to de-escalate violence in eastern Ukraine and saying that US sanctions would remain in place until it withdraws from Crimea.
The recent flare-up in fighting threatens the shaky peace deal that world leaders brokered in the conflict in 2015.
On Friday, international monitor Alexander Hug said ceasefire violations of the Minsk agreement are escalating.
"We have gone from hundreds of ceasefire violations to thousands," said Hug, head of the Organization for Security and Co-operation in Europe's mission in Ukraine, at a briefing at the Avdiivka-Yasynuvata-Donetsk airport area.
The OSCE said it has monitors on the ground in both Donetsk and Avdiivka following the reports of civilian casualties.
The Ukraine crisis has become the bloodiest European conflict since the wars over the former Yugoslavia in the early 1990s.