Ukraine says Russia is waging a "gas war" against Europe, by once again reducing supplies into Germany.
Since the invasion of Ukraine, Western countries have sanctioned Russian oil and gas, prompting warnings of retaliation from Moscow.
How much Russian gas does Europe use?
Russia supplied the EU with 40% of its natural gas last year.
Germany, Europe's largest economy, was the largest importer in 2020, followed by Italy.
The UK imported just 4% of its needs from Russia and the US doesn't import any gas from Russia.
However, they are also affected when Russia restricts supplies to mainland Europe, as this causes global gas prices to rise. Gas prices have almost doubled in the UK over the last year.
What sanctions are in place on Russian gas?
The EU says it will cut gas imports from Russia by two-thirds within a year, but has stopped short of a total ban.
To help reach its goal, member states have agreed to cut gas usage by 15% over the next seven months.
However, there's doubt over where the EU will find alternativesupplies.
"It would have to turn to producers such as the US and Qatar, which would ship liquefied natural gas (LNG) in tankers," says energy advisor Kate Dourian.
"But there aren't enough LNG terminals in Europe. This will be a problem for Germany, particularly."
How has Russia responded?
President Vladimir Putin has demanded that "unfriendly" nations in Europe pay for gas in Russian roubles. This helps support the value of Russia's currency.
Poland, Bulgaria and Finland refused to do so and Russia cut off their supplies.
Several European energy companies are paying for gas via Russian bank accounts, which convert euros into roubles. They insist those payments are in line with sanctions.
Will Europe run short of oil?
The EU has agreed to ban all Russian oil imports which come in by sea by the end of this year.
It will allow oil to continue to be imported by pipeline. EU leaders say this is a "temporary measure" because countries like Hungary and Slovakia depend on it.
The US has declared a complete ban on Russian oil imports. The UK is to phase out Russian oil imports by the end of the year.
Many European nations could have their oil supplies squeezed by the ban.
Lithuania and Finland got about 80% of their oil from Russia in November last year, the latest data available.
However, EU countries can buy oil from other producers.
The IEA - a club of oil importing countries - has released 120m barrels-worth of crude from their stocks.
US President Joe Biden ordered a major release of oil from America's reserves.
"Nations like Saudi Arabia might start putting more oil onto the world market later in the year, and there could be more supplies from the US," says Kate Dourian.
Will sanctions work?
Helped by soaring energy prices, Russia received an estimated €400bn ($430bn, £341bn) over the past year from oil and gas exports to Europe.
The EU says its latest sanctions could cut the amount of oil it buys from Russia by 90%. However, this will take several months to come into full effect, and even then Russia will be able to sell oil elsewhere around the world.
"Countries in Asia might buy up to one million barrels per day more crude oil from Russia than they are taking now," says David Fyfe, chief economist with energy data firm Argus Media.
"As a result of all the sanctions announced so far, Russia may lose between one third and a half of its total oil revenues, but not all of them."
What will happen to my heating and fuel bills?
Consumers are facing rising energy and fuel bills as sanctions on Russian energy kick in.
Heating prices are likely to increase even further if Russian gas exports to Europe are restricted.
In the UK, household energy bills have been kept in check by an energy price cap.
They are expected to reach more than £3,200 when the cap is increased again this autumn.
UK petrol and diesel prices have also soared, and the government has announced a cut in fuel duty as motorists struggle with record prices.