Fighting between Russia and Ukraine has persisted for four years. The conflict has remained deadlocked, with both sides conducting repeated drone and missile strikes on power grids, transport networks, and civilian areas across Ukraine.

The hostilities have extended their reach into wider continental Europe through non-traditional and indirect channels, beyond the territory of the two nations directly involved. Reports indicate that Russia has employed so-called hybrid warfare tactics against European nations, combining unconventional methods across multiple operational domains. The approach seeks to neutralise and undermine a rival's capabilities while stopping short of outright conflict.

Drone strikes targeting Leipzig Airport in Germany were carried out by Russia the previous month. A series of hostile incidents targeting nations including Germany and Romania has been described by some observers as an undeclared campaign against Western countries, with analysts noting the possibility of further escalation.

From the outset of the conflict in February 2022, Russia has employed a variety of methods in its operations against NATO's European member states. Reported incidents have encompassed acts of sabotage, attempts on individuals' lives, and coordinated digital intrusions targeting power networks and communications infrastructure. Undersea cable networks belonging to NATO have also been targeted in physical attacks.

The incidents occurred within what analysts describe as the ambiguous space between open armed conflict and covert hostility. Such actions were atypical, lacked direct attribution, or stopped short of armed confrontation. The Nord Stream gas pipeline attack in September 2022 illustrates one such instance of this category of incident.

Two of the main underwater natural gas pipelines connecting Russia and Germany via the Baltic Sea were struck, halting the flow of energy through those conduits. Prosecutors in Germany have pointed to Ukraine as responsible, though the question of culpability remains disputed among different parties.

In 2021, allegations arose that Russia and Belarus had deliberately directed migrants from the Middle East toward the borders of European Union member states. According to available accounts, the initiative was allegedly conceived to destabilise adjacent nations and led to fatalities among those attempting to cross borders.

Hybrid warfare activities attributed to Russia against European nations have increased in the period since. Data from the United States Congressional Research Service showed that Russian hybrid incidents across Europe rose fourfold between 2023 and 2024, while a separate investigation documented at least 151 such operations from February 2022 through March 2026.

From suspected arson at defence manufacturing facilities to reported interference with civilian navigation and aviation systems through GPS disruption, Russia has been attributed with an expanding pattern of covert activity. Each carries the capacity to cause multiple civilian casualties. Such activities remain consistent with hybrid warfare tactics, given that plausible deniability and the absence of clear attribution continue to function as defining features of the operational approach attributed to Russia.

Their conduct has been placing the unity of allied partners under growing strain. Chancellor Friedrich Merz, speaking in response to the Leipzig Airport incident, stated that those responsible would face consequences and that the country had become an increasingly frequent target of such attacks. The country's administration has formally attributed responsibility for the incident to Moscow.

Russian attacks have been directed at Romanian territory as well. European Commission President Ursula von der Leyen, responding to reports that Romanian forces had intercepted an unmanned naval vessel near a Black Sea oil platform, said the EU and its infrastructure were being subjected to a deliberate campaign of pressure. The latest episode came after a prolonged period of unmanned aerial vehicle violations of Romanian airspace, along with a pattern of drone attacks in areas near the country's border.

Non-combatant populations have been affected. A Russian drone struck a residential building in Romania in May 2026, leaving two people with injuries. The incidents point to a broader pattern of direct armed engagement by Russian forces.

The alliance has expanded aerial surveillance and patrol operations over its eastern flank. In line with its mutual defence obligation under Article 5 — the principle that an assault on one member nation constitutes an assault on all — the alliance has deployed additional air defence systems to member states along vulnerable borders. These measures complement the alliance's pre-existing responses to covert activities, including acts of sabotage and other unconventional destabilisation tactics attributed to Russia.

Three NATO exercises — Baltic Sentry, Eastern Sentry and Arctic Sentry — are designed to strengthen the alliance's defensive posture across land, air and maritime domains.

Russia's covert campaign against Western nations over their backing of Ukraine is reported to have evolved beyond its initial hybrid tactics. Some analysts have argued that the alliance should formally communicate to Russia that actions resulting in civilian casualties or widespread destruction would be treated as equivalent to a direct military assault. Such a development would activate the alliance's mutual defence obligations.

Previously, alliance heads indicated that coordinated hybrid operations could constitute an act of armed aggression. That boundary is open to debate, given US President Donald Trump's repeated expressions of scepticism toward NATO and partner nations. On multiple occasions, he has questioned the alliance's mutual defence commitments, suggesting a reluctance to uphold protections for member states. He has repeatedly played down the perceived threat posed by Russia.

Some analysts have characterised Moscow's recent actions as a probe of the alliance's cohesion and commitment. Hostilities have been ongoing without a formal declaration, with the frequency of attacks on the rise. With Trump's dedication to the organisation remaining uncertain, analysts have said it is unclear how the strained circumstances will develop going forward.