Ukraine’s western Rivne region went through “a very difficult night” and “suffered a powerful enemy airstrike,” Oleksandr Koval, head of the regional military administration, wrote on Telegram. One person was injured, he said. He did not provide further details.

Monday’s attack appeared to have caused less damage than one on Friday, which Kremlin officials said was in response to an audacious Ukrainian assault on air bases inside Russia earlier in the week. In Friday’s bombardment, Russian drones and missiles hammered Kyiv and cities in western Ukraine, causing extensive damage and injuring dozens.

Monday’s strike took place as Moscow’s forces claimed to be advancing toward Ukraine’s southeastern Dnipropetrovsk region — an area of the country that has been heavily bombarded but so far has avoided ground fighting.

Kremlin spokesman Dmitry Peskov said the offensive was in part an attempt to create a “buffer zone.”

However, Andriy Kovalenko, head of the Ukrainian military’s Center for Countering Disinformation, posted on Telegram that “all information from the Russians, including Peskov’s statements, about their offensive on the Dnipropetrovsk region is NOT true.”

The Russian advance could represent a further intensification of Moscow’s military pressure across the front line, which has now spread to Ukraine’s northeastern Sumy region.

In his regular evening address, Ukrainian President Volodymyr Zelensky said Sunday that in “some areas” along the front line, “the situation is very difficult.” Fighting is underway in the Donetsk, Sumy and Kharkiv regions, he added.

On Monday, Zelensky announced on Telegram the beginning of a prisoner exchange that would “continue in several stages in the coming days.” Zelensky said he could not divulge all details but that the first group included those who were seriously wounded and under the age of 25.

“The process is quite complicated, there are many sensitive details, negotiations continue virtually every day,” Zelensky wrote.