The EU said Monday it is urgently discussing a new round of sanctions on Russia as it condemned "atrocities" reported in Ukrainian towns that have been occupied by Moscow's troops.

The European Union "will advance, as a matter of urgency, work on further sanctions against Russia," foreign policy chief Josep Borrell said in a statement on behalf of the bloc.

"We stand in full solidarity with Ukraine and the Ukrainian people in these sombre hours for the whole world," he said.

One EU official told AFP that a new sanctions package on Russia would be discussed this week. EU foreign ministers could then look it over, either on the sidelines of a NATO meeting happening Wednesday and Thursday, or at their regular meeting early next week.

Borrell said in his statement that the EU "condemns in the strongest possible terms" the atrocities reported in Ukrainian towns that had been occupied by Russian forces, including the town of Bucha, where corpses were found with their hands bound.

"The massacres in the town of Bucha and other Ukrainian towns will be inscribed in the list of atrocities committed on European soil," Borrell said.

He said that "the Russian authorities are responsible for these atrocities, committed while they had effective control of the area".

The statement stressed EU assistance to Ukrainian prosecutors "focused on collection and preservation of the evidences of the war crimes" and its support of probes launched by the International Criminal Court and the UN's human rights commissioner.