Four Czech citizens were apprehended by the police after they were caught taking pictures near a weapons factory and arms depot in Poliçan, in southern Albania.
The incident took place at around 8:40 am on Sunday after the Czech nationals were detected in one of the tunnels at the facility, the country's Ministry of Defence said in a statement.
The suspects have been taken in for questioning and the four are claiming to be tourists, Euronews Albania reported.
The regional police director, military police representatives and at least two vehicles of the rapid intervention force, FNSH, have all been seen arriving in the region's capital, Berat.
The arrest of the four Czechs took place after two Russians and a Ukrainian were caught in a similar incident at a military plant Gramsh, also in southern Albania.
The Russian man, the 24-year-old Mikhail Zorin, was detained after entering the plant's grounds in Gramsh, 80 kilometres south of the capital, Tirana, and taking photos, the ministry said in a statement.
Two military guards were injured by what is alleged to be a type of paralysing agent or pepper spray used by the Russian while resisting arrest.
Another Russian woman, the 33-year-old Svetlana Timofoeva, and a Ukrainian man identified by initials only, F.A., 25, were arrested outside the complex, and their vehicle was blocked, the ministry said.
The vehicle has since been identified as an orange Chevrolet muscle car with Ukrainian licence plates.
"Three persons were accompanied by police which in cooperation with other institutions is investigating the case," the statement said, adding that military police, army intelligence police and civil and anti-terror police are coordinating on the case.
The two army guards injured by the spray were taken to a military hospital for medical care and have since been released.
"What pride for the military guards who neutralised three individuals suspected of espionage," Prime Minister Edi Rama wrote on Twitter, adding: "Now let's wait for the full clarification of this event."
The two arrests seem to be unrelated, despite Gramsh and Poliçan being in the same area of southern Albania and only 90 kilometres apart.
The three suspects arrested in Gramsh claim that they are "bloggers photographing Communist-era buildings", local media reported.
The Gramsh military plant opened in 1962 to produce licenced copies of AK-47 Kalashnikov rifles.
After the fall of communism in 1990, it stopped production and instead began to dismantle old Kalashnikovs and other small weapons. It also repairs other army weapons.
The facility is currently being tested for conversion to produce 5.56mm NATO rounds, domestic media reported.
The factory in Poliçan also made Kalashnikovs in the past, while it now manufactures 7.62mm ammunition. Rifles and pistols produced in the former Soviet Union and its satellite states, such as AK-47 and Tokarev, are commonly made in this calibre.
Albania, a NATO member since 2009, has strongly renounced Russia's invasion of Ukraine and has joined European Union and U.S. sanctions against Moscow.