The Morrison government has expressed dismay at a diplomatic deal between Ukraine and Russia that has freed one of the key suspects in the downing of Malaysian Airlines Flight MH17 over Ukraine more than five years ago.

Foreign Affairs Minister Marise Payne took issue with the prisoner-swap between the two countries because it included Vladimir Tsemakh, who was facing questioning in Ukraine over the MH17 attack but will be repatriated to Russia and may escape any penalties.

Relatives of Ukrainian prisoners freed by Russia greet them upon their arrival un Ukraine. Credit:AP

United States President Donald Trump welcomed the deal between Ukraine and Russia as "very good news" and "perhaps a giant step to peace" but Australia has taken a different approach by warning against the inclusion of Mr Tsemakh.

Once he is in Russia, Mr Tsemakh may not be available to investigators from a team backed by the Dutch and Australian governments.