The former Swedish prime minister considers Russia's invasion of Ukraine as 'insane'.

• While it would be "unthinkable" for Russia to invade Ukraine, it is "not inconceivable," according to Carl Bildt, a former prime minister of Sweden.
• The military presence of Russia at the border of Ukraine has been increasing, leading to growing tensions and fears of an escalation between the two countries.
• Bildt stated that Europe's war and peace landscape, as well as security, would be ventured into unknown territory.

While it would be "insane" for Russia to invade Ukraine, the possibility of this happening is not "impossible," according to former Prime Minister of Sweden Carl Bildt.

Although a massive invasion is unlikely, it's not entirely impossible, according to Bildt, who is now a co-chair of the European Council on Foreign Relations, given that Russian President Vladimir Putin has used military power against Ukraine in the past.

He stated on CNBC's "Capital Connection" on Thursday that it would be insane, as there would be media broadcasts of explosions and images of refugees fleeing in the event of an invasion.

He predicted that the impact on Russia's economy and society would be significant, prompting individuals to rally resources to aid Ukraine.

Bildt stated that Europe's war and peace landscape, as well as security, would be ventured into unknown territory.

He remarked that the decision-making circles in the Kremlin are beginning to understand the reality of potential outcomes.

Recent military buildup by Moscow at the border between Russia and Ukraine has sparked concerns of an impending war. Despite negotiations with the U.S. and other Western powers, little progress has been made, prompting Washington to urge a diplomatic solution.

The Kremlin has denied any plans to invade Ukraine, repeating its illegal annexation and occupation of Crimea in 2014.

Since the start of the year, Russian assets have declined more than 11% due to the impasse.

Europe’s gas supplies at risk?

The Nord Stream 2 pipeline, which has the capacity to transport 55 billion cubic meters of natural gas to Europe annually, has frequently been proposed as a potential bargaining chip against Russia.

But the former Swedish prime minister isn’t hopeful.

He informed CNBC that the project cannot be utilized in negotiations because it is predicted to become operational only in the latter part of 2022.

He stated that he believes it is not useful as a negotiating tool and expressed greater concern about Nord Stream 1, which has the same transportation capacity.

If Germany is cut off from Nord Stream 1, it will face a critical situation, he stated.

Approximately 43% of Europe's gas imports come from Russia, as stated by Eurostat.

Europe's gas supplies will be threatened in two scenarios, as stated by Bildt.

If there is fighting and an invasion into Ukraine, it would be challenging to see that the pipes will deliver gas just meters below the tanks rolling and shooting on the ground, as stated by him.

"Russia may retaliate against heavy Western sanctions by cutting gas flow, which is the only forceful and dangerous action they can take," he said.

He stated that the possibility of a detrimental effect on Europe is still being discussed.

The Biden administration is considering strategies to ensure energy supplies for European allies if Russia decreases its oil and gas exports.

The Russian economy requires revenue as much as Europe needs its energy supply, according to a senior administration official.

The official stated that Putin's advantage is not asymmetrical; rather, it is an interdependency.

— CNBC’s Amanda Macias and Silvia Amaro contributed to this report.