Serbia gets its oil supply mainly via Croatia and the Adriatic Sea, a link that will be severed when the EU enforces a ban on Russian seaborne crude from December.

However, Hungary will still receive Russian oil via the Druzhba (Friendship) pipeline, which is exempt from the EU ban.

"The new oil pipeline would enable Serbia to be supplied with cheaper [Russian] crude oil, connecting to the Friendship oil pipeline," Hungarian government spokesman Zoltán Kovács said earlier this week.

Kovács said the project was part of a long-term ambition from Hungary to diversify the region's energy infrastructure.