(CNN) An Australian father who lost three children in the downing of Malaysia Airlines Flight 17 has lashed out at President Donald Trump for his relationship with Russia, on the fourth anniversary of the tragedy.

The plane had been above Ukraine territory controlled by pro-Russian separatists, and investigators in May said the missile had been fired by a Russian brigade. Russia has repeatedly denied involvement in the incident.

In a Facebook post on Tuesday, Maslin lambasted Trump's unwillingness to condemn Russia, accusing him of ignoring "irrefutable facts."

"That passenger flight MH17 was shot out of the sky and 298 innocent people were murdered is an irrefutable fact," Maslin wrote.

"That the plane was hit by a Russian missile has been proven to be an irrefutable fact."

"That the man whose arse you've just been kissing did this, and continues to lie about it, is an irrefutable fact."

"I miss them I miss them I miss them underlies everything," she wrote of her three children.

"I am Grief. This is me. Grief is me."

Calls for justice

The posts come amid a national outcry in the US over Trump's reluctance to confront Russian President Vladimir Putin over his country's alleged interference in the 2016 US presidential election.

At the Helsinki summit on Monday, Trump declined to endorse the US government's assessment that Russia interfered in the 2016 presidential election and instead appeared to side with Putin, leading to a wave of criticism from Democrats and Republicans alike.

Russian President Vladimir Putin and US President Donald Trump shake hands before a meeting in Helsinki, on July 16.

The political controversy came as leaders worldwide spoke out to commemorate the fourth anniversary of MH17 and demand accountability.

The G7 foreign ministers condemned the shooting down "in the strongest possible terms."

"We fully support the work of the Joint Investigation Team (JIT), an independent criminal investigation led by the Netherlands, Australia, Belgium, Malaysia and Ukraine," the statement read. "The JIT's findings on Russia's role in the downing of MH17 are compelling, significant and deeply disturbing."

"We are united in our support of Australia and the Netherlands as they call on Russia to account for its role in this incident and to cooperate fully with the process to establish the truth and achieve justice for the victims of MH17 and their next of kin."

The wrecked cockpit of MH17 during an investigation report on October 13, 2015.

Australian Foreign Minister Julie Bishop also issued a statement on Tuesday expressing her condolences to the families of the victims. 38 of the victims on board were Australian.

"On 25 May 2018, Australia and the Netherlands announced that we hold Russia responsible for its role in the downing. We hope that through negotiations with Russia we can open dialogue around the circumstances leading to the tragic loss of innocent lives," Bishop wrote.

"We owe that to the memory of the victims and their families and friends."

The Russian government has repeatedly disputed those allegations, and has suggested instead that Ukrainian forces shot the plane down with either a surface-to-air missile or one of their own fighter jets.