Dutch investigators probing who is to blame for the downing of Malaysia Airlines flight MH17 two years ago have pressed Russian authorities to hand over outstanding evidence, officials said Thursday.

Initial results from the criminal inquiry into who shot down the ill-fated flight over eastern Ukraine on July 17, 2014 killing all 298 passengers and crew on board are expected to be revealed after the summer.

"The Russian authorities have supplied information before, but have not answered all the questions," the Dutch Public Prosecutor's office said in a statement after a two-day visit to Moscow on Tuesday and Wednesday.

"The outstanding requests have now been discussed," the statement said.

Fred Westerbeke, chief investigator in the criminal probe told the respected NRC daily in an interview that Dutch investigators made a "pressing request" to the Russians to hand over outstanding information.

"We told them that time was of the essence," Westerbeke told the newspaper.

Moscow has said before that it did not have so-called "primary radar information" which Dutch prosecutors hoped could help pinpoint exactly where the surface-to-air missile was fired from that brought down the passenger flight, carrying mostly Dutch citizens.

Westerbeke told the NRC that based on "analysis" it is believed that additional radar information may be available, hence the request to Moscow.

"The Russians will now look into whether additional information is available or not," Westerbeke said.

In October, an international inquiry concluded that the Boeing 777, which was en route from Amsterdam to Kuala Lumpur, was shot down by a Russian-made BUK surface-to-air missile fired from a zone held by pro-Russian separatists, but stopped short of saying who was responsible.

Results of the latest investigation will not be published in a report, however, but will be included in a criminal file "which is intended for the hearing of the case in a court or a tribunal," the prosecutor said, indicating this was normal procedure in criminal cases.

The European Union in early July formally extended damaging economic sanctions against Russia by six months due to lack of progress resolving the conflict in eastern Ukraine.

The measures target the oil, financial and defence sectors of the Russian economy and were first imposed after the shooting down of flight MH17.