Russia's President Vladimir Putin spoke with Luxembourg's Prime Minister Xavier Bettel on the phone about the war the Kremlin is waging against Ukraine.

Putin, in an attempt to justify his military's actions, referred to the "incessant rocket attacks by Ukrainian forces on Donetsk and other cities in the Donetsk People's Republic and the Luhansk People's Republic, which have led to many civilian casualties," a Kremlin statement said on Saturday.

The Russian leader has been internationally condemned for his military's invasion of Ukraine, which has frequently featured attacks on civilian sites.

Putin and Bettel had already spoken last Monday.

According to a statement by the Luxembourg Ministry of State, Bettel's aim was to contribute to the 24-day-old conflict's de-escalation.

Bettel was quoted in the statement as saying that he was especially troubled by the deteriorating situation in the encircled port city of Mariupol and that he was deeply shocked by attacks on civilian facilities.

"The images reaching us are unbearable," Bettel said.

He and Putin had agreed to stay in contact, he said.