Germany is seeking to extradite a suspect from Romania over the discovery of an underground stash of weapons in a forest near Berlin that German media reports have linked to Russian intelligence.

Two weeks after German authorities found a drone carrying explosives at Leipzig airport, the interior minister, Alexander Dobrindt, confirmed federal prosecutors had opened an investigation related to the secret cache of guns “on suspicion of preparing a serious act of violence that threatens national security”.

“This case demonstrates that ‌we are operating under a high threat level,” he told reporters. As with the Leipzig incident, Dobrindt said he could not rule out the involvement of “foreign powers”.

Earlier, local media had reported that German authorities had unearthed two handguns and ammunition about a year ago in a wooded area outside the German capital after agents of the domestic intelligence service received a tip.

The find has been the focus of covert investigations by state security and counterespionage services on suspicion Russian intelligence was plotting assassinations on German soil, according to separate reports by Der Spiegel magazine and an investigative team led by Süddeutsche newspaper.

Rather than removing the arms, German authorities left them on site after rendering them unusable in the hope they would lead to clues during a months-long electronic surveillance operation, Dobrindt said.

No one was observed trying to collect the weapons, leading investigators to believe the agent or agents had learned of the cache’s discovery and it was now “dead”.

Dobrindt described the suspect in Romania, whose nationality was not disclosed, as a “low-level agent” and noted several other such operatives had ‌been detained so far this year.

Although the investigation into the Berlin stash has been long-running, the revelations apparently led Dobrindt to hastily call the news conference on Friday.

Sinan Selen, the head of the Federal Office for the Protection of the Constitution, Germany’s domestic intelligence agency, has warned for months of more aggressive tactics by Russian secret services including plans for targeted attacks on German soil.

Moscow’s potential hit list is believed to include weapons contractor executives, opposition figures in exile and other prominent Ukraine supporters, according to the report by Süddeutsche and the public broadcasters NDR and WDR.

The federal prosecutor’s office and the Russian embassy declined to comment. A BfV spokesperson said “as a matter of principle, we don’t comment on matters relating to any specific intelligence activities”.

Spiegel said German authorities were looking into possible links between the arms cache – a familiar Soviet tactic during the cold war – and a sabotage campaign against Ukrainian logistics routes blamed on Russia.

Last year Polish security officials arrested several people allegedly planning to mail parcels containing incendiary devices or detonators, some of them reportedly to have been posted from Romania.

Investigators believe the packages could have been remotely ignited or set off using timers during transit to do serious damage to vehicles, cargo planes or logistics centres and spread fear in the EU.

In 2024, a firebomb in a parcel posted via DHL exploded in a freight container on the tarmac at Leipzig airport. Only a delayed flight kept it from going off in the air.

Ukraine has been using the facility in Leipzig as an alternate location for the transport of military goods since the start of Russia’s full-scale invasion in February 2022, according to official records.

This month the German newspaper Die Zeit reported that Russian secret services were plotting an attack against Stefan Thumann, the head of German drone manufacturer Donaustahl.

The report said German investigators were tipped off by a foreign intelligence service at the end of last year and arrested a Ukrainian man and a Romanian woman this spring.

Thumann is said to be under police protection. The case recalled reports in 2024 that US intelligence services had foiled a Russian plot to assassinate the chief executive of Germany’s leading arms manufacturer, in an apparent attempt to retaliate over the company’s role in providing armaments for Ukraine.

The plan to murder Armin Papperger, the chief executive of Rheinmetall, was reportedly one of several Russian government schemes to kill defence industry executives in several countries in Europe that have been supporting Ukraine’s war effort. The plot against Papperger was believed to be the most advanced.

Russia has repeatedly denied any involvement in sabotage, disruption or intimidation against EU member states.