Britain accused Russia on Saturday of making false claims about the Malaysian airliner that crashed in eastern Ukraine and said it was "highly likely" it was brought down by a Russian-supplied missile fired from a Russian-backed separatist area.
The Foreign Office said in a statement that Russia had issued a succession of contradictory claims and denials about the crash, which killed all 298 people on board, including 10 Britons.
Britain was also aware of information that suggested separatists had been planning to scatter parts of other aircraft on the site to hinder investigators, it said.
The statement came after Russia's ambassador to Britain, Alexander Yakovenko, told reporters on Thursday that allegations Russia was involved in the downing crash "didn't hold water".
The Foreign Office statement, entitled "Russian myths on MH17," dismissed Kremlin assertions that it only provides humanitarian assistance to the separatists and that Western evidence to the contrary lacked credibility.
"Given the large and growing body of credible evidence, without compelling information to the contrary, we believe it is highly likely that that flight MH17 was shot down by the Russian SA-11 surface to air missile system, operating from within a Russian-backed separatist area in eastern Ukraine," it said.
"Russia has made a number of contradictory, mutually-exclusive claims which blame Ukraine for this attack, but they have no basis in fact," it added.
"Russia has not provided any evidence to support its claims."
The statement said that journalists at the scene have reported that Russian-backed separatists were preventing access to the site by investigators, deliberately tampering with the crash site, moving bodies and stealing the personal possessions of victims.
"It added, without elaborating: "Worryingly, we are aware of information suggesting that separatists were planning to scatter parts of other aircraft on the site."
Ambassador Yakovenko said on Thursday it was too early to lay blame over the crash. Western attempts to involve Russia were based on social media reports rather than hard evidence, he added.
Russia has called for the investigation into the crash to be carried out by the United Nations International Civil Aviation Organization (ICAO).