The Ukrainian Security Service (SBU) has released audio purporting to show pro-Russian militants in eastern Ukraine discussing receipt of sophisticated antiaircraft weapons and the crews to man them from Russia.

The SBU believes the weapons were used to shoot down a Malaysia Airlines passenger jet on July 17, killing some 300 people.

The first of the newly released conversations purportedly took place on July 14 between a commander in the self-proclaimed "Luhansk People's Republic" and an alleged officer of Russian military intelligence (GRU) by the nickname of "Oreon."

In that conversation, the Luhansk commander says, "We already have the Buk and we will shoot them [Ukrainian military planes] down" and Oreon responds, "Yes, I know that."

In another conversation also reportedly recorded on July 17, Khmury and another Donetsk commander discuss what to do with the new Buk-M. Khmury orders the Buk and a small detachment of men to establish a position near the Ukrainian village of Pervomaysk.Buryat tells Khmury that the Buk-M "came through the stripe," referring to the security cordon along Ukraine's border with Russia.

In a final conversation, also purportedly recorded on July 17, Khmury tells yet another Donetsk commander that "we have received a Buk-M."

"Thank God, this morning the Buk-M arrived and the situation has gotten a little better," he says, "although it is still pretty tough."

On July 17, the SBU released audio recording they claimed were intercepted calls among eastern Ukrainian militants proving that they shot down the Malaysian airliner.