Bristling with security cameras and surrounded by a solid steel and marble fence with barbed wire, Sobieskiego 100 is just one of several buildings that is occupied by Russia following agreements signed between the People's Republic of Poland and the Soviet Union in the 1970s.
A Polish citizen, detained by Polish security agency on suspicion of spying for Russia, has pleaded guilty to the charge.
Internal Security Agency spokesman Stanisław Żaryn said the two suspects were also interacting with organised crime and that “the actions of the Russians are aimed at using information tools to attack Poland and carry out activities against the interests of the Republic of Poland.”
The presidents of the Bucharest Nine, a group of countries forming Nato's eastern flank, point out "permanent threat" from Russia, Polish President Andrzej Duda said after the group's summit in Bucharest on Monday.
The US should be more strongly committed to the Three Seas Initiative, comprising countries between the Baltic Sea, the Adriatic and the Black Sea, according to the Polish prime minister.
Polish President Andrzej Duda on Tuesday met with visiting Estonian President Kersti Kaljulaid to discuss military and energy security as well as green solutions for the two countries' power systems.
The Visegrad Group will jointly take further steps within the EU and Nato to convince Russia that attacks on other countries are costly, Poland’s deputy foreign minister has said.
The prime ministers of the Visegrad Group (V4) in a joint declaration on Monday backed the Czech Republic in its diplomatic conflict with Russia.
The EU supports Poland in its diplomatic strife with Russia, which has culminated in the recent expulsion of five diplomats from the Polish embassy in Moscow.
The Polish Foreign Ministry has described Russia's decision to expel Polish diplomats as another example of aggressive politics.