KYIV, March 9 - The trial has opened in the Netherlands of three Russians and a Ukrainian - still at large - for the murder of 298 people aboard Malaysia Airlines flight MH17, shot down over Ukraine in 2014, BBC reported.

The Boeing 777 went down amid a conflict in eastern Ukraine, after Russian-backed rebels seized the area.

Investigators say they have proof the Buk missile system that shot it down came from a military base in Russia.

A judge called it an "atrocious disaster", as proceedings began.

The trial is in a court near Amsterdam's Schiphol airport, the departure point for the Kuala Lumpur-bound flight.

Head judge Hendrik Steenhuis said there had been a "tragic loss of human lives from all around the world".

Russia has repeatedly denied involvement in the deadly attack on July 17 2014. Citizens of 10 different countries died on the airliner.

The three Russian men and one Ukrainian man from eastern Ukraine are all linked to the heavily armed pro-Moscow separatists.

Neither country extradites its citizens but one of the Russians will have a defense team in the courtroom, and the court says it is also prepared to accept testimony from them by video link.

This trial is the culmination of the most complex criminal investigation in Dutch history.

Two thirds of the victims were Dutch; the Netherlands took the lead in the investigation and the trial will be held within the Dutch legal system.

Two weeks have been allocated for the start, which will cover mostly procedural aspects and establish whether indeed the trial will be conducted in absentia, without the accused.

Unconfirmed Dutch reports say there are 13 witnesses whose identities will remain secret, but the judges may decide that anyone who has already given evidence to prosecutors may not need to appear in person.

The court will be able to hear anonymous testimony if necessary, in a trial that could take more than three years.

Two of the suspects allegedly have ties to Russia's GRU military intelligence agency, which has been linked to cyber-plots as well as the deadly nerve agent attack on Salisbury in England.

The four men are:

Igor Girkin, also known as Strelkov. He is a former colonel in Russia's FSB intelligence service, given the title of minister of defense in the rebel-held eastern Ukrainian city of Donetsk, prosecutors say.

Sergei Dubinsky, known as Khmury. He was employed by Russia's GRU military intelligence agency, according to investigators. They say he was a deputy of Girkin and in regular contact with Russia.

Oleg Pulatov, known as Giurza. He is allegedly a former soldier with GRU special forces who became deputy head of the intelligence service in Donetsk. Pulatov will be represented by a defense team, so the court may decide he is not considered in absentia.

Leonid Kharchenko, known as Krot, is a Ukrainian national with no military background who led a combat unit as a commander in Eastern Ukraine, say prosecutors.

The four are accused of murdering 298 people and causing the MH17 crash. Prosecutors say the men are jointly accountable for the attack because they "co-operated to obtain and deploy" the Buk missile launcher in order to shoot down an aircraft. (bbc/ez)