The crisis in Nagorno-Karabakh has come amid a sharp deterioration in the relationship between historic allies Armenia and Russia, and has been amplified by sometimes incendiary commentary from prominent individuals in Moscow.

Armenia’s prime minister has called his country’s security relationships “ineffective,” in a swipe at Russia after Azerbaijan claimed the breakaway province of Nagorno-Karabakh following a swift military campaign.

The cause of the blast is unclear, but a Nagorno-Karabakh presidential aide said initial reports indicated it was due to negligence.

Tens of thousands of ethnic Armenians rushed on Wednesday to flee the breakaway region of Nagorno-Karabakh for Armenia after a lightning military operation by Azerbaijan that has recast the contours of the post-Soviet South Caucasus.

Nagorno-Karabakh - recognised as part of Azerbaijan - had been run by ethnic Armenians for three decades. The mountainous region in the South Caucasus has been supported by Armenia - but also by its ally,

Azerbaijan sent troops backed by artillery strikes into Armenian-controlled Nagorno-Karabakh on Tuesday in an attempt to bring the breakaway region to heel by force, raising the threat of a new war with its neighbour Armenia.

The explosion at a fuel storage facility near the regional capital of Stepanakert wounded more than 200 people, Nagorno-Karabakh human rights ombudsman Gegham Stepanyan tweeted. It was not immediately clear what caused the blast,