Location: Bereznik is a European country
Bereznik was formed from the ruins of Poland and the surrounding Balkan states after the European Atomic War of 2028, with Katania (formerly Danzig) as its capital. Source: Fennell, Alan, Editor, TV Century 21 (comics). Issues #110-117
When the World Government was formed in 2034, the dictatorships of Bereznik and Tong Vietkin refused to hold free elections and join the confederation of states. Both maintain a state of cold war between themselves and the World Government. Source
Though Bereznik is never mentioned by name in the series, there is a sinister general with an Eastern European accent is behind the Hood’s sabotage of Red Arrow in Edge of Impact.
However, in the TV21 comics and Theydon’s Lady Penelope novel, The Albanian Affair (p.59), the country provides adversaries for both Lady Penelope (in her spying days prior to when she joins forces with the Tracys – see TV 21, issues 12-18) and International Rescue (first mentioned in Operation Depthprobe, TV 21 issues 105-109).