Oil prices have surged past $100 (£74) a barrel after Russian President Vladimir Putin launched a “special military operation” in the eastern Donbas region of Ukraine.
These are the highest levels seen by the international benchmark Brent crude futures in more than seven years.
Prices jumped earlier this week before cooling amid economic sanctions and moves to block a Russian gas pipeline.
Russia is the second biggest exporter of crude oil after Saudi Arabia.
It is also the world’s largest natural gas exporter.
“We could see prices keeping the momentum,” said Tina Teng, a markets analyst at CMC Markets.
“Investors are concerned about an even tighter supply, caused by the US sanctions on Russia to target the key supply source, the Nord Stream 2 gas pipeline,” she told the BBC.
Nord Stream 2 is a 1,200km pipeline under the Baltic Sea, which will take gas from the Russian coast near St Petersburg to Lubmin in Germany.
The pipeline does not yet have an operating licence – and Germany has now put this on hold.
It took the step after Russia formally recognised two breakaway regions in eastern Ukraine, and sent troops there.
The US, UK and some of their allies have also imposed a series of sanctions on Russia in response to Mr Putin’s actions against Ukraine.
The UK has frozen the assets of five banks and three Russian billionaires, who have also been hit with travel bans.
On Tuesday, Boris Johnson said these sanctions were a “first barrage” and could be extended.
“The moves by Russia suggest economic sanctions are not having any significant impact in holding off aggression,” said Yeap Jun Rong, a market strategist at IG.
“With retaliation measures coming from Western powers soon, it seems that the situation may show no signs of easing,” he added.