Russia’s President Vladimir Putin is threatening to reduce gas supplies to Europe this winter.

Speaking in Serbia, he warned of the move should Ukraine siphon off gas from a transit pipeline to cover its own needs. Moscow turned the taps off to Kyiv in June in a row over unpaid bills.

“If we observe that our Ukrainian partners, as in 2008, begin removing gas without permission from the export pipeline system, then we, as in 2008, will reduce the volume of exports in proportion to the volume of gas stolen by Ukraine,” Putin said.

His warning has substance. Russia is Europe’s biggest gas supplier, meeting around a third of the region’s demand. And the EU gets about half of the Russian gas it uses via Ukraine.

Putin was guest of honour at a rainy military parade in the Serbian capital as troops, tanks and fighter jets marked seven decades since the Red Army liberated Nazi-occupied Belgrade.

Before thousands of onlookers, more than 3,000 soldiers marched in the city’s first military parade since 1985, when it was the capital of socialist Yugoslavia. Tanks rumbled behind them and jets tore through the rainy skies above.

Serbia, which began negotiations this year on joining the 28-nation EU, has refused to join the West’s Ukraine-linked sanctions imposed on Russia, despite EU pressure to align its foreign policy.