The Ukrainian incursion into Russia’s Kursk region – the largest since the war began, with around 1,000 troops and more than two dozen tanks and other armored vehicles storming across the border this week – poses a threat to a key gas supply pipeline from Russia to the European Union.

Although it may come as a surprise to many given the war in Ukraine, European countries such as Austria, Hungary and Slovakia are still buying gas from Russia – and all of that gas flows through the town of Sudzha in Kursk.

Here’s everything you need to know about what’s at stake for Europe, why EU member states still rely on Russian gas, and how this latest twist in the war could affect supplies.

Where in Russia did Ukraine launch its attack?

Kyiv sent hundreds of soldiers, supported by armored vehicles, artillery and drones, across the Ukrainian border into the Kursk region on Tuesday. According to the Institute for the Study of War, a US think tank, Ukrainian troops had advanced up to 35 kilometers into Russia by Thursday, reaching Kromskiye Byki and Moljutino.

The Kremlin was completely taken by surprise and declared a state of emergency. Thousands of residents were evacuated and reinforcements were immediately sent to the region. At the same time, influential “milibloggers”, pro-Russian military bloggers, accused the military leadership of “strategic miscalculations” that had put the population in western Russia in danger.

On Friday, fighting was reported near a nuclear power plant in the town of Kurchatov. The facility is of strategic importance because Ukrainian forces could use the plant as leverage or simply shut down its operations, depriving Russia of a vital source of electricity.

But the impact of the attack on energy supplies extends far beyond Russia. Just 70 kilometers from Kurchatov, fighting has been reported near Sudzha, near a pipeline that carries Russian natural gas to the EU.

Why is Sudzha so important for Europe’s gas supply?

Sudzha is located about 10 kilometers from the Ukrainian border and plays a key role in natural gas transit to the EU.

An average of 42 million cubic meters (1.5 billion cubic feet) of Russian gas flows into Ukraine every day. The city has a gas metering system that measures supplies flowing to Europe.

Despite the war with Russia, Kyiv allowed gas to flow freely through its Soviet-era gas pipeline under a $2 billion-a-year deal between state-owned Naftogaz and Russian Gazprom.

From Ukraine, the gas is routed towards Slovakia, where it branches off; one of the branches leads to the Czech Republic, the other to Austria.

The transit contract expires in January. If there are disruptions to gas supplies before then, gas prices could skyrocket and hit European consumers and industry hard.

What is the current situation in Sudzha?

On Friday, pro-Russian military bloggers reported heavy fighting on the outskirts of Sudzha.

The Center for Information Resilience (CIR), a nonprofit open-source analytics organization, said it had verified footage showing several Russian soldiers surrendering to Ukrainian soldiers near the entrance to the gas detection facility in the city.

Although it appears “likely” that the power plant was affected by the collapse, the CIR added that it was unable to verify the extent of the damage.

So far, the hostilities do not appear to have had any impact on gas supplies to Europe.

Christoph Halser, an analyst at Oslo-based energy company Rystad Energy, told Al Jazeera that output fell 5.8 percent to 37.25 million cubic meters (1.3 billion cubic feet) on Thursday and rose 3.2 percent to 38.5 million cubic meters (1.36 billion cubic feet) on Friday.

On Thursday, Ukrainian Energy Minister German Galushchenko announced that the transit route was still functioning. On the same day, Gazprom and Naftogaz said operations were continuing as usual.

Why does Europe still import Russian gas?

“In the short term, it has limited other options,” says Mike Coffin, head of oil, gas and mining research at the London-based think tank Carbon Tracker.

“While Western Europe can rely on LNG (liquefied natural gas) and the North Sea, these options are less open for parts of Central Europe,” he told Al Jazeera.

According to Halser, the share of Russian gas in total European imports has more than halved, from 38 percent in 2021 to 15 percent in 2023.

However, the countries remain highly dependent on Russian gas, which is routed via Ukraine, “due to the historical development of pipeline infrastructure,” he said.

In 2018, Austria’s OMV signed a long-term supply contract with Gazprom for the delivery of more than 6 billion cubic meters (212 billion cubic feet) per year until 2040.

And Hungary’s MVM has committed to supplying 4.5 billion cubic meters (160 billion cubic feet) annually by 2036. Most of this will be delivered through the TurkStream pipeline via Turkey.

Jade McGlynn, a Ukraine expert and research fellow at King’s College London, said: “Some European countries are still importing Russian gas because they want the best of both worlds. They are not prepared to bear the political costs of moving away from Russian gas more quickly.”

This could cause disruptions in energy markets and trigger price increases that would be extremely unpopular with voters.

According to them, these countries have so far refused to provide air defense systems to protect Ukraine’s energy infrastructure, thus representing an important source of income for Russian military spending.

McGlynn believes that if there were any supply disruptions at this stage of the all-out war, they would “have only themselves to blame.”

Could Russia turn off the tap?

Analysts point out that Gazprom could possibly use the fighting as a pretext to interrupt gas supplies.

However, if exports were stopped, the country would lose around $4.5 billion annually, assuming an expected average gas price to Europe of $320 per 1,000 cubic meters (35,300 cubic feet) in 2025.

Halser said that due to “Russian commercial interests” it was unlikely that oil supplies would be stopped “unless there is physical damage or conditions change on the Ukrainian side.”

In 2022, when Russian forces launched their full-scale invasion of Ukraine, Naftogaz stopped the flow via an alternative branch line in Sokhranivka, near the Luhansk region in eastern Ukraine.

Ukraine said at the time that Russian forces had begun diverting gas to Luhansk and the breakaway Donetsk region.

After the closure of Sokhranivka, the transit volume of Russian gas via Ukraine to the EU fell by a quarter.

Does Europe need to find another source of gas supplies?

Whatever the outcome of the current idea, the contract between Naftogaz and Gazprom in its current form expires at the end of the year.

The Slovak gas supplier SPP said that after the contract expires, a consortium of European gas buyers could take over the gas at the Russian-Ukrainian border. How this will work, however, is still unclear.

Another possibility is for Gazprom to supply part of the gas via another route, for example via TurkStream, Bulgaria, Serbia or Hungary. However, the capacity via these routes is limited.

The EU is trying to diversify its gas imports and has signed an agreement to double imports of Azerbaijani gas to at least 20 billion cubic meters per year by 2027. But infrastructure and financing are lacking, according to an adviser to the Azerbaijani president quoted by Reuters news agency.

It is also expected that as domestic consumption in Azerbaijan increases, spare capacity for Europe will decrease.

In any case, the long-term goal should be to move away from fossil fuels, said Coffin of Carbon Tracker.

“To reduce dependence on imported Russian gas, Europe needs to further diversify electricity generation, increase the share of non-fossil energy sources while reducing energy demand and modernizing electricity grids,” he said.

“European countries should work together in this regard to reduce overall demand rather than focusing only on their own needs.”