Relatives of MH17 crash victims, angered by what they see as Dutch mishandling of inquiries into the disaster, want a special U.N. envoy to launch an international investigation.

A letter sent to Prime Minister Mark Rutte on Friday said Dutch officials had failed to build a case. They asked that inquiries by the Safety Board and prosecution service be handed over to the United Nations.

Rutte should "request the U.N. to appoint a special envoy to take over," said the letter, written by Van der Goen Attorneys.