A court in Ukraine on Thursday released from pre-trial detention a man suspected of involvement in the downing of flight MH17, amid speculation he may be used in a prisoner swap with Russia.

Ukraine captured Vladimir Tsemakh, accused of fighting for pro-Russian separatists, in June, but he is believed to be a person of interest in the downing of MH17. European lawmakers described him as a "key suspect" and asked Kiev to make him available for testimony in the probe.