AMSTERDAM (Reuters) - Dutch prosecutors have opened an investigation into the crash of Malaysia Airlines flight MH-17 on suspicion of murder, war crimes and intentionally downing an airliner, a spokesman said on Monday. Based on the Law on International Crimes, the Netherlands can prosecute any individual who committed a war crime against a Dutch citizen. The 298 people who were killed when the plane was downed over Ukraine included 193 Dutch citizens.

The spokesman said that a Dutch public prosecutor was in Ukraine as part of the investigation.

The Dutch prime minister meanwhile threatened tough action against Russia if it did not do more to help.

Western governments have pointed the finger of blame at pro-Russian rebels and at Moscow itself over the downing of the plane. Russia has denied involvement and blamed the Ukrainian military for the disaster.

"It is clear that Russia must use her influence on the separatists to improve the situation on the ground," Prime Minister Mark Rutte told a committee of the Dutch parliament.

"If in the coming days access to the disaster area remains inadequate, then all political, economic and financial options are on the table against those who are directly or indirectly responsible for that," he said.

His comments reflected a change in tone from previous days, when he had stressed the importance of ascertaining the facts of the crash before considering a response.

Rutte on Monday promised lawmakers "measures would not be lacking" if it was confirmed who was responsible for bringing down the airliner.

Rutte's remarks followed days of mounting pressure calling on the government to take a harder line against Russia.

"In the Netherlands we are inclined to approach our opponents in a fair and socially acceptable way in hope that opponents will respond in kind," said Dick Berlijn, a former head of the Dutch armed forces who has been outspoken in calling for a tougher approach.

"What we have seen, especially with the Russian administration is this didn't impact at all, they saw this as a weakness," he said in an interview with Reuters.

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Russia, is the Netherlands' second-largest oil supplier and a major export destination for Dutch manufacturers. But growing consternation over the fate of flight MH-17 and its passengers may be forcing the government into taking a harder line.

On Monday afternoon, relatives of some of the passengers who lost their lives met Rutte alongside the Dutch King and Queen to be briefed on efforts to recover their bodies and to allow them to give their views on what sort of a memorial service should be held.

(Reporting By Thomas Escritt, editing by Angus MacSwan)