One resident told Russian state news agency RIA Novosti her husband was in their bedroom in the building when the blast went off and was injured in the head and face. "He did not have the time" to escape, she said.

A spokesperson for the Russian Investigative Committee said a criminal case has been launched.

The incident comes as "intense battles" continue just across the border in north-eastern Ukraine, where Russian forces have made incursions into the Kharkiv region.

In his evening address on Sunday, Ukrainian President Volodymyr Zelensky said the Russian offensive has displaced thousands.

"The idea behind the attacks in the Kharkiv region is to stretch our forces and undermine the morale and motivation of the Ukrainians' ability to defend themselves," he added.

The defence ministry in Moscow claims its forces have captured a number of villages there, while Kyiv says it has been carrying out counter-attacks.