Self-styled pro-Russian separatist kingpin Igor Strelkov captured the attention of the world today when he appeared to claim responsibility for the downing of Malaysian Airlines flight MH17.

A social media site linked to Strelkov said insurgents had shot down an army transport plane near where the Boeing 777 was shot down with the loss of nearly 300 lives.

The comments by the top military commander of the self-proclaimed "Donetsk People's Republic" suggested the separatists shot down the Malaysia Airlines plane by mistake, believing it was a large Ukrainian army transport plane.

So who is Igor Strelkov - the man known as Igor the Terrible?

Born Igor Girkin in 1970 and raised in Moscow, he is said to hold a strong attachment to historic Russia with a desire to see the re-emergence of a Russian empire.

During his time as leader of militant groups in Ukraine he has established a reputation for forceful rule and ruthless justice - condemning Western societies as "decadent".

Western intelligence agencies say he is a former agent in Russia's Main Intelligence Directorate.

The moustachioed Strelkov emerged as a leader of armed rebels during the fighting in Crimea earlier this year.

He established a base in Slaviansk, where he was accused of kidnapping, torturing and murdering a local Ukrainian politician and a 19-year-old student.

On April 15 Ukraine's Security Service opened criminal proceedings against Strelkov, describing him as a Russian recruiter and accusing him of leading a campaign of "terror" in and around Slaviansk.

From there Strelkov headed towards Donetsk and Luhansk in eastern Ukraine, rallying pro-Russian rebel groups in the area under the banner of the "Donetsk People's Republic".

He has claimed responsibility for shooting down a plane on Thursday via European social media site VK.

"We just downed an AN-26 near Torez. It is down near the Progress Mine" said the VK page attributed to Mr Strelkov.

On Thursday a Twitter account for the "Donetsk People's Republic" issued several posts claiming to have seized a missile system from the Ukrainian army.

"@dnrpress: self-propelled Buk surface-to-air missiles systems have been seized by the DNR from (Ukrainian) surface-to-air missile regiment A1402," the Twitter post said.

Military analysts say the Buk medium-range surface-to-air missile is the weapon most likely to have been used to shoot down MH17.

A post attributed to Mr Strelkov was issued, and later removed, from the account saying "We warned you, do not fly in our sky".

"And here is a video confirming that a 'bird fell'," the post concluded, linking to a video showing locals watching a pall of black smoke rising over trees on the horizon.

ABC/AFP