It was supposed to be the evidence that proved beyond doubt Moscow's assertion that Washington is supplying Ukraine with weapons in its fight against pro-Russian separatists in the east.

A statement released on Wednesday by the "general prosecutor's office" of the self-proclaimed Lugansk People's Republic reported the discovery of a US weapons cache, including a Stinger missile system, in the rubble of the war-torn region's wrecked airport.

"The American MANPAD Stinger was already in the operational service of the Ukrainian Armed Forces a year ago," the Lugansk prosecutors said.

Their accompanying video showed the supposed US portable rocket launcher with the words "tracking rainer" -- "rainer" apparently being a misspelling of "trainer" -- printed on the side.

But on Thursday Russia's alogvinov.com video game site claimed that the supposedly incriminating footage had been taken from a video game.

The site noted that "trainer" was misspelt in exactly the same manner on a popular video game called Battlefield 3.

The Russian site noted several other odd spellings that appeared to support its assertions about the origin of the footage.

Wednesday's allegations by the rebels had been reported by several Russian news sites. There was no immediate response to the apparent forgery from the Lugansk militia leaders or their official information agency.

Moscow and Kiev have been waging a furious propaganda since fighting erupted in the east following the popular overthrow of Ukraine's Russia-backed president 15 months ago.

One of the most infamous bogus allegations made by the rebels was detailed in a BBC expose in April.

The reporter found locals who confirmed that a 10-year-old girl whom the rebels said died in the shelling by government forces of a village in the rebel-held region of Donetsk had, in fact, never existed.

The rebels responded by stripping the BBC reporter of the accreditation required by insurgency leaders to cover the war.

Washington accuses Moscow of orchestrating and supporting the separatists but so far has publicly refused Kiev's demands for heavy weapons, restricting its support to non-lethal equipment such as bullet proof vests and radar.