A German fraud investigation company says an anonymous client has provided US$30 million as a reward for information and evidence leading to the culprits behind the Malaysia Airlines Flight 17 disaster over eastern Ukraine.

The plane, heading to Kuala Lumpur from Amsterdam, went down on July 17 over territory held by pro-Russian rebels. All 298 passengers and crew on board were killed.

Last week, the chief Dutch prosecutor overseeing the criminal investigation said the "most likely" scenario is that Flight MH17 was shot down from the ground.

The German company, Wifka, says it has been charged with finding out who shot the plane down and who gave the order.

Wifka said the reward money is “securely deposited” in Zurich, Switzerland, and will be paid out there or “in a different neutral place of the whistle-blower’s choice.”

The company also said its mysterious client is offering to give the whistle-blower a “new identity.”

Wifka said those interested in the reward should “take great care” and contact them through a lawyer, without giving away details by email or over the phone.