The giant Ust-Luga complex, located on the Gulf of Finland about 170 km (110 miles) west of St. Petersburg, is used to ship oil and gas products to international markets. It processes stable gas condensate - a type of light oil - into light and heavy naphtha, kerosene and diesel to be shipped by sea.

According to Reuters, it was not clear how long the disruption would last, how many tankers would have to idle outside the port, and what the knock-on effect would be on international energy markets.

The Interfax-Ukraine news agency said the fire was the result of a special operation carried out by Ukraine's security services.

"The Ust-Luga Oil terminal in the Leningrad region is an important facility for the enemy. Fuel is refined there, which, among other things, is also supplied to Russian troops," it cited one source as saying. Of course, the fuel is also used to supply Europe where energy prices are now expected to spike as a result of this latest supply disruption.

"A successful attack on such a terminal not only causes economic damage to the enemy, depriving the occupiers of the opportunity to earn money to wage war in Ukraine, but also significantly complicates the logistics of fuel for the Russian military."

While Reuters was not able to confirm that the fire resulted from a Ukrainian drone attack, it writes that if it did "such an attack would demonstrate Kyiv's ability to conduct strikes deeper into Russia than usual using what are believed to be domestically produced drones at a time when it is on the defensive on the battlefield and struggling to secure as much Western financing as it wants."