Ukrainian intelligence said on Wednesday that 144 Ukrainian soldiers, including scores of defenders of the Azovstal steelworks in the southern port city of Mariupol, had been freed in a prisoner swap with Moscow.

"This is the largest exchange since the start of the full-scale Russian invasion. Of the 144 freed, 95 are Azovstal defenders," the main intelligence directorate of Ukraine's defence ministry said on Telegram.

It did not specify when and where the swap took place or how many Russian prisoners were released as part of the exchange.

It added that 43 of the freed servicemen belonged to the Azov regiment, a former paramilitary unit that is now integrated into the Ukrainian army.

Russia considers the unit a neo-Nazi organisation and has previously said its soldiers should stand trial.

Moscow and Kyiv have exchanged prisoners several times since Russia invaded on February 24.

The most recent previous exchange took place on Tuesday and involved 17 Ukrainian prisoners. (AFP)