Ukraine's top commander Oleksandr Syrskyi says he has spent several days on the eastern Pokrovsk front and described fighting there as "exceptionally tough".
Russia has been pressing hard towards the strategic hub of Pokrovsk in recent months, steadily inching forward.
The scale of assaults did not drop after Ukraine launched a surprise incursion into Russia's west Kursk region on August 6.
President Volodymyr Zelenskiy said the situation near Pokrovsk was "extremely difficult" and Ukraine would further strengthen its positions.
"Fights are exceptionally tough. The enemy throws into battle everything that can move and advance, trying to break through our defences," commander Syrskyi said on Facebook, adding that Ukraine had to constantly use unorthodox methods to strengthen its positions.
He said the most intense clashes were taking place in the area of Krasnyi Yar, 10km from the city of Pokrovsk.
Eastern outskirts of Hrodivka village, less than 9km from the strategic route connecting the city to Kostiantynivka, were also seeing intensified assaults, Syrskyi added.
Ukraine's General Staff put the number of clashes in Pokrovsk front at 23 since the start of the day.
Zelenskiy said on Telegram on Thursday he was briefed by his top military on the situation during a meeting that also discussed "concrete defensive actions".
He added that Ukrainian domestically produced long-range weapons were discussed in a separate meeting, as well as the Kursk incursion.
"Operation tasks are being implemented," he added.
The Ukrainian military said on Thursday that one of its F-16 fighter jets crashed while repelling a major Russian attack on Monday.
The jet came down and its pilot died while it was approaching a Russian target, the Ukrainian General Staff said on Thursday on Facebook.
The F-16s had "demonstrated high efficiency" and downed four Russian cruise missiles, it added. U
kraine said Russia launched more than 200 missiles and drones that day targeting the energy sector.
"Connection with one of the aircraft was lost while it was approaching the next target. As it turned out later, the plane crashed and the pilot died," the statement said.
Zelenskiy said on August 4 that Ukraine did not have enough pilots trained to use the F-16s or enough of the jets themselves.
Ukraine's air force western command said on Facebook that pilot Oleksiy Mes died in a combat mission on Monday.
"Oleksiy saved the Ukrainians from deadly Russian missiles. Unfortunately, at the cost of his own life," the statement said.
