The incident happened one day after Russia said it was cutting off gas supplies to Ukraine over a payment dispute. Ukraine is fighting an insurrection in its eastern and southern provinces that it says is being supported and encouraged by Moscow.
Ukraine's Interior Ministry said it was investigating a number of possible causes, including terrorism.
The pipeline, which was completed in 1983, has capacity for 32 billion cubic meters a year and is one of two major gas pipelines that run through Ukraine to Western Europe from Russia. At the site of the blast the pipeline was six metres underground.
"According to locals, just before the fire, they heard two loud bangs that may indicate a deliberate explosion," Ukraine's Interior Minister Arsen Avakov said. . In May, prosecutors opened a criminal investigation into an explosion along the pipeline in western Ukraine, saying there had been evidence of sabotage.
But the local Interior Ministry branch said it appeared the pipeline had "burst," sparking the fire - suggesting it was an accident. Ukraine has been accused in the past of poorly maintaining its Soviet-era pipelines.
The decision by Russia's Gazprom to halt supplies to Ukraine will further destabilise Ukraine's crippled economy, although Ukrainian officials said they had adequate inventories and other supply sources to meet domestic needs at least until the end of the year.
Reader Comments
Amid the manmade calamities, there are signs that are warnings. We had some Lenticular clouds here last week that contained what looked like dark shapes that were winged. They also had rings around them that appeared to be lit with reddish fire. I took them as warnings in the sky, for what is soon to transpire if dark hearts do not relent.