Frustrated relatives of those killed when Malaysia Airlines Flight 17 was shot out of the sky over eastern Ukraine are appealing to the European Union's top diplomat to put pressure on Russia, Ukraine and the United States to hand over intelligence and radar data to investigators.

An international team of investigators is seeking to file criminal charges against those responsible for the downing.

In an open letter Wednesday, relatives say, "For us, as concerned families, it is very important that the perpetrators will face justice."

Flight MH17, from Amsterdam to Kuala Lumpur, was hit by a Soviet-era Buk surface-to-air missile on July 17, 2014, above conflict-torn Ukraine. All 298 passengers and crew onboard were killed.

A spokesman for the investigation declined to comment on progress in the probe.