As Tverečius was geographically part of the Vilnius Region, and subsequently included in the Republic of Central Lithuania, the town became Polish territory in March 1922: Tverečius found itself incorporated as Twerecz, part of Święciany (Lithuanian: Švenčionys) Powiat (county) in the newly created (1926) Wilno Voivodeship, the northeasternmost province then in Poland.
As part of the Soviet invasion of Poland, the Red Army defeated the Poles in the Battle of Wilno, and control of the Vilnius Region was fractured: Vileyka Voblast was a territorial unit in the Belarusian Soviet Socialist Republic created out of the eastern powiats of the Wilno Voivodeship after the annexation of West Belarus (then part of Poland) in November 1939. One of these eastern powiats was Święciany; thus Tverečius found itself included as part of the Belarusian SSR, albeit briefly. When the Soviet Union invaded Lithuania in 1940, Tverečius was transferred from the Belarusian SSR into the newly incorporated Lithuanian SSR.
