Activists from Greenpeace Nordic prevented the ship Coral Energy from delivering a cargo of Russian fossil gas at a liquified natural gas (LNG) terminal in Nynäshamn, south of Stockholm.
Protestors reportedly climbed cranes to unload gas from the ship.
Meanwhile, Greenpeace sailing vessel SY Witness and activists in kayaks are in the water to prevent the ship from docking.
The activist organisation is demanding that Sweden immediately stops the the import of Russian fossil gas.
Karolina Carlsson, campaign leader at Greenpeace Nordic, said: “The fact that Russian fossil gas is still allowed to flow into Sweden, more than six months after Putin began his invasion of Ukraine, is unacceptable.
“The Parliament has given the Swedish government a clear mandate to stop all imports of Russian energy to Sweden and it is Prime minister Magdalena Andersson’s obligation to act on this.”
Sweden has received around 100.000 cubic meters of liquefied fossil gas (LNG) from Vysotsk in Russia.
Greenpeace claim that Sweden continues its imports of gas despite an announcement from its Parliament that it needs to stop.
The Riksdag said in an online statement: “The Riksdag emphasizes that it is important that the government continues to clearly and forcefully push the line in the EU that European dependence on Russian energy should end as soon as practically possible.
“This applies not least to fossil energy. The government should also pursue the issue of the EU developing a regulatory framework for origin labeling of fossil energy, which primarily concerns geographical origin.
“Measures also need to be taken so that Sweden stops importing Russian energy whenever possible, not least fossil fuels such as natural gas and oil.”
Nadia Shevchenko, Ukrainian journalist and environmental expert who is on board the Greenpeace sailing vessel Witness in Nynäshamn, said: “I am extremely grateful for all the support that Sweden has given to Ukraine in these dark times for my country.
“At the same time, it is incomprehensible to me how Sweden’s government can support Ukraine with one hand and with the other finance Putin’s invasion and the abuse of the Ukrainian people by allowing these imports of Russian fossil gas to continue.”
Ms Shevchenko moved to Sweden with her daughter after a Russian bomb exploded near her home in Kyiv.
However, the envinromental activist said the first thing she saw when she arrived was a tanker ship unloading 27 million euros worth of Russian gas.
Speaking to Express.co.uk, a currency expert said that despite the efforts of Western sanctions, the Russian economy was ultimately being kept afloat by its sales to “gas-guzzling Europe”.
Greenpeace added: “This peace protest is, like all Greenpeace actions, a safe and peaceful protest carried out with the highest priority on the safety of activists, personnel and equipment in the area.
“All activists are experienced climbers and use ATEX-rated equipment for work in dangerous environments.
“The activists also have measuring equipment to ensure that they are not exposed to any dangerous substances when they are in the area.”