The blast rocked the Druzhba pipeline in the Russian-backed separatist city of Lugansk, Russia’s RIA Novosti state news agency said.

The incident, the causes of which remain unclear, occurred during a sharp escalation in fighting that has redoubled fears that Russia is preparing to invade Ukraine.

The Druzhba pipeline runs from Russia to various points in eastern and central Europe.

Images on social media showed a bright orange fireball lighting up the night sky.

Russian state media reported a second blast in Lugansk less than an hour after the one that appeared to hit the pipeline.

Its causes were not immediately clear, but a social media account associated with the Lugansk separatists said the second blast hit a petrol station on the city’s outskirts.

There were no immediate reports of casualties from either blast.

The region around the city of Lugansk has witnessed some of its heaviest fightings since the start of the year in the past two days.