Russia has threatened to use nuclear weapons against the United Kingdom if the NATO country attempts to cut off or attack Russia’s exclave of Kaliningrad.

The statement follows a miniseries aired by British broadcaster Sky News last week, The Wargame, which traces a hypothetical Russian attack on the U.K. and how the country might respond—including by authorizing operations against the Baltic territory of Kaliningrad.

Referencing the simulation and media reports, Moscow’s embassy in the U.K. said on Tuesday: “Those advocating plans to blockade or strike Kaliningrad should have no illusions about the consequences.”

“Any British or NATO military action against Russian territory would be met with a response using all means at Russia’s disposal, including nuclear weapons,” the Russian embassy said.

Newsweek has reached out to the U.K. foreign office for comment via email.

The statement marks the latest dip in heavily strained relations between London and Moscow, shortly after the U.K.’s top naval official, General Sir Gwyn Jenkins, called Russia the “greatest threat” to British security.

“We know that Russia is probing us for weakness,” Jenkins, the head of the country’s Royal Navy, said earlier this month.

A top Russian official, Yulia Zhdanova, claimed this month that NATO countries were “already testing specific scenarios for blockading” Kaliningrad.

U.K.-Russian relations are now at their worst point since the early days of the Cold War, said John Foreman, a former U.K. defense attaché to both Moscow and Kyiv.

“It’s been downhill since 2014,” Foreman told Newsweek. Moscow annexed the Crimean Peninsula from Kyiv in 2014 and backed pro-Kremlin separatists in Ukraine’s eastern Donbas region.

Russia still controls these territories, and the U.K. says it has provided at least £16 billion (about $21 billion) in military aid to Ukraine since the start of Russia’s full-scale invasion of its neighbor in February 2022.

The U.K.’s relationship with Russia “plunged after 2022,” Foreman added.

The U.K. has become increasingly willing to publicly confirm when it tracks Russian ships and submarines near its coastline, including ships linked by Western officials to sabotage of critical undersea infrastructure, like cables and pipelines.

In June, the U.K. seized one of Russia’s “shadow fleet” vessels for the first time, which Moscow uses to skirt sanctions slapped on its oil exports. British commandos clambered onto the Smyrtos, surrounded by military helicopters and two warships, as it traveled in international waters.

Russian President Vladimir Putin accused the U.K. of “piracy and banditry.”

Meanwhile, in March, Russia expelled a top British diplomat from the country over spying allegations, which the U.K. government described at the time as “complete nonsense.” Another British official had been ordered to leave Russia in January.

No replacement Russian ambassador to the U.K. has been appointed since the previous envoy, Andrey Kelin, left London in July.

The Alarm Bells Are Ringing Louder

Russia has the world’s largest nuclear arsenal, just ahead of the U.S. Combined, Moscow and Washington control roughly 90 percent of all nuclear weapons.

The Kremlin says it has no plans to attack NATO soil, despite warnings from alliance officials that Moscow could launch some form of assault on NATO as early as before the end of 2026.

Russia also insisted it had no plans to invade Ukraine just before Russian tanks poured over the border into the neighboring country over four and a half years ago.

But NATO officials say Russia is intensifying its hybrid warfare attacks on its members, referring to a range of activities stopping short of open fighting. These can include cyberattacks, information campaigns or targeting vulnerable infrastructure like power grids or undersea cables.

NATO has said Russian fighter jet flights near airspace controlled by its members have surged, widely seen as an intimidation tactic.

Denmark’s defense intelligence service said last week Moscow could carry out a limited attack on one or more NATO countries bordering Russia in the next few months to weaken support for Ukraine and deal a blow to NATO unity.

The risk of this scenario is “low but growing,” Danish intelligence said.

The stark Danish assessment came less than two months after a Wall Street Journal report said the U.S. believed the Kremlin could attempt a small-scale land grab—often considered the realistic worst-case scenario—or dramatically increase its hybrid warfare campaign from this fall.

Analysts say that if Russia did move to occupy part of NATO territory, it would probably amass soldiers close to Estonia, Latvia or Lithuania’s eastern borders or push into an area known as the Suwałki Gap.

Why Is Kaliningrad So Important?

Kaliningrad is sandwiched between Poland and Lithuania on NATO’s eastern flank, and a contentious strip of land, the Suwałki Gap, links the isolated Russian oblast to Belarus. The territory, which sits on the Baltic Sea, is home to a major Russian naval fleet and launchers able to fire fast-traveling missiles.

All the other countries bordering the Baltic Sea are NATO members, earning it the nickname of a “NATO lake.”