Dutch prosecutors had the opportunity to interview a person of interest in the Malaysia Airlines flight MH17 missile attack before a prisoner swap between Ukraine and Russia.
Foreign minister Stef Blok has told the chair of the lower house of the Dutch parliament that the government had been informed in mid-August that the person involved, named as Vladimir Tsemach, might become part of the prisoner exchange.
Blok says the Dutch prosecution service had "done everything possible" through judicial channels to keep Tsemach available for questioning by criminal investigators probing the destruction of the Boeing 777-200ER over Ukraine in July 2014.
He adds that the government "urged" the Ukrainian authorities not to make Tsemach part of the prisoner swap, to avoid his transfer to Russia. Russian-backed personnel are suspected to have been involved in the surface-to-air missile launch which shot down MH17.
Blok says the Ukrainian side offered to "postpone" the exchange to give Dutch prosecutors the opportunity to interview Tsemach again, and adds that this questioning subsequently took place.
But he stresses that the Dutch government "deeply regrets" the inclusion of Tsemach in the 7 September swap.
Some 35 Ukrainian citizens were released from Russia under the agreement, returning on a Ukrainian government Antonov An-148.
Investigators directing the criminal probe into MH17's loss have previously identified four individuals – three Russians and a Ukrainian, none of which is Tsemach – who they are seeking to prosecute over the attack.