Russian forces are pushing into EU and NATO territory through hybrid warfare tactics including surveillance, airspace violations and psychological operations — and increasingly in the digital realm.
That is what a German soldier deployed in Lithuania experienced when he answered his phone and heard his own voice — a chat he’d had just hours earlier — by an unknown caller.
“A comrade phones home, speaks for half an hour, and then gets a call from an unknown number. He answers – and hears his own conversation from earlier, recorded and played back,” Joshua Krebs described the experience in his book, Inside Bundeswehr.
Krebs called this kind of intimidating surveillance “uncanny”.
European armed forces, including the Bundeswehr, are encountering similar hybrid activity at home as well.
Drones have been used to allegedly spy on sensitive defence systems, such as the Arrow 3 air defence system, as well as on exercises involving Germany’s Battletank Brigade 45 in Lithuania.
Last year, a Russian reconnaissance aircraft was detected in neighbouring Belarusian airspace during the Bundeswehr exercise Iron Wolf in Lithuania.
The German Army’s Inspector General, Carsten Breuer, described the incident as “proof of the very real threat to Lithuania”.
Federal Defence Minister Boris Pistorius (SPD) also stressed that hybrid warfare is a particular concern for Lithuania when he met his Lithuanian counterpart in Berlin at the end of January.
According to Pistorius, the threat posed by Russia is felt more acutely in Lithuania and across the Baltic region than elsewhere in Europe, for example through provocative airspace incursions.
Airspace violations: provocation or oversight?
Pistorius was referring to an incident in October 2025, when two Russian fighter jets briefly entered Lithuanian airspace.
According to the Lithuanian armed forces, they remained there for around 18 seconds before turning back, escorted out by NATO aircraft. German Chancellor Friedrich Merz (CDU) described the incident as yet another Russian provocation.
The jets are thought to have come from Russia’s Kaliningrad exclave, which borders Lithuania directly.
Given the Baltic states’ close proximity to Russian territory on more than one side, the airspace over the region is considered especially sensitive and is under constant NATO surveillance and protection.
Germany, Spain and the UK are currently leading the mission to police Baltic airspace, as Estonia, Latvia and Lithuania do not have fighter jets of their own.
Germany is also playing a direct role on the ground. “Among other things, Germany is supporting the protection of Lithuanian airspace with a mobile air force command post for air surveillance from January to March this year,” Pistorius said in January.
‘Little green men’ in the Baltic states stir fear
There were no real consequences after the incident, not least because hybrid warfare exists in something of a legal grey area. It is often unclear at what point an action amounts to an attack, when a response is justified and, above all, what that response should look like.
A major difficulty is the lack of clear proof – both in terms of the actual impact and of who is responsible. Unlike the brief incursion by Russian fighter jets into foreign airspace, many hybrid activities cannot be directly attributed to a single actor.
Even so, the intention is broadly understood to be the same: to provoke, to unsettle and to sow fear. The reaction is usually similar too – expressions of concern, condemnation, and calls for it to stop.
When Russian border guards crossed into NATO territory in Estonia without authorisation in December last year, Tallinn responded through diplomatic channels, simply requesting an explanation from Moscow and convening a meeting between Russian and Estonian border officials.
It was not an isolated episode. A few months earlier, a group of armed men in military-style uniforms – but without any insignia – had been spotted near the Estonian border.
Incidents of this kind recall the so-called “little green men” who appeared on Ukraine’s Crimean peninsula in 2014. Shortly afterwards, Moscow illegally annexed Crimea, which remains under Russian occupation to this day.
The unidentified soldiers did not advance any further into Estonian territory. According to experts, the October incident was largely seen as a psychological tactic rather than a credible military threat.
Instead, it appeared to be a show of presence – a way for Russia to signal that it is there and to keep nerves on edge.
When is it legitimate to respond?
In principle, international law is clear on one central point. Under Article 2(4) of the UN Charter, states are prohibited from threatening or using force against one another. Conventional military attacks clearly fall within this definition.
Hybrid activities, however, do not automatically qualify as an “armed attack” in the legal sense – the threshold that would trigger a state’s right to self-defence under Article 51 of the UN Charter.
Instead, each case has to be judged individually, and different areas of law may apply depending on the nature and severity of the incident.
International law also applies here, including the general principle that states must not interfere in the internal affairs of others.