NIEUWEGEIN, NETHERLAND: Relatives of those killed when flight MH17 was shot down over Ukraine exactly a year ago joined emotional memorials on Friday as calls mounted for a UN-backed tribunal to prosecute those responsible for the tragedy.

All 298 passengers and crew -- the majority of them Dutch -- died on July 17 last year when the Malaysia Airlines Boeing 777, on a flight from Amsterdam to Kuala Lumpur, was downed over rebel-held east Ukraine during heavy fighting between Kiev's armed forces and pro-Russian separatists.

Flags flew at half-mast in the Netherlands as about 2,000 relatives and friends gathered at a ceremony in Nieuwegein to mourn the victims of the disaster, many of whom were children on their way to summer holidays.

Kiev and the West point the finger at the separatists, saying they may have used a BUK surface-to-air missile supplied by Russia to down the plane. But Moscow denies involvement and instead accuses Ukraine's military.

"There is nothing we can do, we can't turn back the clock," said Evert van Zijtvelt, who lost his son, Robert-Jan, 18 and daughter Frederique, 19, in the disaster. "It has been a very heavy year."

The widow of the flight's co-pilot, Ahmad Hakimi, told the Dutch ceremony that her husband had refused her pleas to stop working after the mysterious disappearance of Malaysia Airlines Flight MH370 in March 2014.

"I begged my husband not to go to work because I was afraid but he told me 'this is my job, it is my duty, I have to do it'," said Asmaa Aljuned.

Sobs could be heard as relatives read out the names of all those killed and photos of the dead were shown on a giant screen accompanied by sombre piano music.

Dutch Prime Minister Mark Rutte assured the bereaved that justice would be done.

"The investigation into what exactly happened and everything that still needs to be done will be to do right by your loved ones," Rutte told the black-clad gathering.

The commemoration held a minute's silence exactly one year after air traffic control lost contact with the flight.

In Canberra, Australian Prime Minister Tony Abbott unveiled a plaque in memory of those killed, including 38 Australian citizens and residents.

"Today we remember our dead, we thank those who brought them home. But most of all, we acknowledge the suffering of the bereaved," he told the crowd, which included 120 relatives of those who perished.

Australian Paul Guard, who lost his parents Roger and Jill, made the journey to the Australian capital with nine other family members.

"It will be a difficult day but hopefully a useful part of the healing process," he told reporters.

Malaysian relatives also took part in a memorial service in Kuala Lumpur last week, demanding justice and answers about who is responsible for the disaster.

At the crash site in eastern Ukraine, around 200 villagers gathered to remember the day bodies and plane parts came crashing down from the sky.

The locals -- mostly bussed in by separatists -- waved flags of the self-proclaimed Donetsk People's Republic and carried banners accusing Kiev of killing innocent people in the ongoing battle with the rebel forces.

"You were killed. But we are still being killed," read one banner.

As relatives struggle to come to terms with their grief, the focus is shifting to tracking down the perpetrators and putting them on trial.

Ukraine's President Petro Poroshenko said it was a "moral duty" to punish the "murderers".

The Netherlands has been tasked with leading the retrieval of victims' remains and investigating the cause of the crash, as well as finding and punishing possible perpetrators.

Apart from two passengers, both Dutch, the remains of all other victims have been found and positively identified.

The Dutch Safety Board is expected to release a final report into the cause of the crash during the first week of October, but has stressed it will only address the cause, not the perpetrators.

The board released a preliminary report last September saying damage to the plane's forward fuselage and cockpit section appeared to "indicate that there were impacts from a large number of high-energy objects from outside".

A criminal probe by a joint investigation team consisting of Australian, Belgian, Dutch, Malaysian and Ukrainian detectives is under way.

The UN Security Council has adopted Resolution 2166, which demands those responsible "be held to account and that all states cooperate fully with efforts to establish accountability".

Britain, France, Malaysia, the Netherlands and others have backed a UN-backed tribunal, but veto-wielding Security Council member Russia is opposed.