A fire at a factory producing combat drones in Poland was caused by sabotage, the country's Prime Minister Donald Tusk said on Wednesday.
Speaking ahead of a Cabinet meeting in Warsaw, Tusk said there is no doubt that this was a deliberate act of arson.
He added that arson could not be ruled out in another fire at a factory producing components for the aviation industry in Lublin, although clear evidence was as yet lacking in that case.
On Monday, a fire broke out at the WB Electronics factory in Skarżysko-Kamienna, some 150 kilometres south of Warsaw. No one was injured.
WB Electronics is the country's largest private defence contractor and a supplier to the Polish army.
The public prosecutor's office is investigating on suspicion of terrorism and acting on behalf of a foreign intelligence service aiming to the detriment of Poland.
The broadcaster Rmf.fm reported that the company's CCTV cameras are said to show a man wearing a balaclava and carrying a rucksack, who is alleged to have started a fire in one of the rooms. The intruder is also said to have triggered the alarm system.
On Sunday, a fire broke out in a production and storage hall belonging to the company JFG Composites near Lublin in the east of the country. The manufacturer makes components for the aviation industry.
Poland - an EU and NATO member state - is a key political and military supporter of Ukraine, which is under attack from Russia. It also feels threatened by Moscow and is significantly ramping up its military capabilities.
Warsaw accuses the Russian and Belarusian intelligence services of sending numerous agents into the country to carry out acts of sabotage.