Security agencies and governments across Europe are increasingly warning about the threat posed by Russia-directed saboteurs operating on their territories.

On Wednesday, Norway’s Police Security Service (PST) and the Norwegian Intelligence Service (NIS) warned there was an increased threat of sabotage targeting organizations in the country involved in delivering arms to Ukraine.

Inger Haugland, Norway’s counterintelligence chief, told the media how attempts at sabotage in Poland, Germany and the United Kingdom were conducted by non-Russian nationals to provide the Kremlin with deniability.

Haugland said the PST had warned Norwegian arms suppliers to be on alert for suspicious activity, as reported by the country’s national broadcaster NRK. Earlier this month, the head of the PST warned that Russia was preparing acts of sabotage in the west of the country where its naval bases and oil and gas facilities are based.

The pair of warnings follows Norway’s Prime Minister Jonas Gahr Støre describing Russia as posing “a real and serious threat” to the country’s oil and gas industry, following the arrests of seven Russians in Norway in connection to incidents in which drones were flown over major energy installations.

Elsewhere in Europe, three arrests in Poland were announced this week, with Prime Minister Donald Tusk saying that the country’s security services had caught suspected saboteurs whom they believed were directed by Russia’s intelligence agencies.

The three arrests add to the nine detentions of suspected members of a Russian espionage ring last year, which Polish authorities believed was also preparing acts of sabotage. The arrests in Poland have included two men suspected of hacking the national railway’s communications network, and a professional ice hockey player who is accused of conducting espionage for Moscow.

The uptick in arrests and warnings follows NATO and the European Union condemning “intensifying” Russian sabotage and hybrid operations earlier this month.

The North Atlantic Council, NATO’s political executive, announced that allies were “deeply concerned about recent malign activities on Allied territory, including those resulting in the investigation and charging of multiple individuals in connection with hostile state activity.”

The European Council, the EU’s political executive, subsequently alleged that a cyber campaign attributed to Russia’s military intelligence service showed “Russia’s continuous pattern of irresponsible behavior in cyberspace, by targeting democratic institutions, government entities and critical infrastructure providers across the European Union and beyond.”

Amid these concerns, the Sueddeutsche Zeitung reported that explosives were discovered buried near an oil pipeline in Germany this week.

The concerns about Russia’s sabotage operations extend well beyond the Kremlin’s neighbors. 

In the U.K., two British nationals have been arrested within the past few weeks on suspicion of an arson attack against a Ukrainian-owned business in London, allegedly directed by the Kremlin. Separately, the U.K. has charged six Bulgarian nationals suspected of spying under the direction of the Russian state.

The British government cited the spying case when it announced earlier this month what it called a “major package of measures to target and dismantle Russian intelligence gathering operations” in the country, including removing the diplomatic premises status of an estate in the country allegedly used by Russian intelligence officers to meet agents.

Anne Keast-Butler, the head of the cyber and signals intelligence agency GCHQ, said earlier this month that British officials were “increasingly concerned about growing links between the Russian intelligence services and proxy groups to conduct cyberattacks,” warning that the Kremlin’s partnership with criminal groups was also contributing to “suspected physical surveillance and sabotage operations.”