Abu Dhabi, United Arab Emirates - Russia and Ukraine have agreed to their biggest ever release of prisoners after two days of US-mediated talks in Abu Dhabi, US envoy Jared Kushner said Wednesday.

"One of the positives is we agreed that we're going to have the biggest humanitarian release of prisoners, which we're going to finalize the numbers tomorrow," Kushner said.

Kushner and fellow US mediator Steve Witkoff will travel to Moscow on Thursday to meet Russian President Vladimir Putin, and then to Dublin to debrief Ukrainian President Volodymyr Zelensky on the progress of negotiations to end the war.

The two sides have exchanged thousands of captured soldiers throughout the almost five-year war, which began when Russia launched a failed full-scale invasion of Ukraine in February 2022.

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Diplomatic talks have so far failed to move the two sides closer to an agreement to halt the fighting, which has killed hundreds of thousands of people.

The two days of conversations in Abu Dhabi appeared to fit that mould, with the prisoner exchange and agreement to carry on talking the only concrete outcomes mentioned by any side in post-talks press statements.

Russian envoy Vladimir Medinsky and Ukrainian negotiator Rustem Umerov also said a large-scale prisoner exchange had been agreed, adding that exact numbers would be announced at a later date.