Posters were found in a few villages in Assam's Sonitpur district on Sunday, claiming that those belonged to neighbouring Arunachal Pradesh, officials said.
The incident comes days after the two states signed an agreement to resolve the longstanding border disputes between them.
The posters, printed on white paper, had 'ABPF' written at the bottom -- an organisation not known earlier, officials said.
These posters were found in Daflagarh, North Karibil, Nalinibari and Mangalbaria in Helem sub-division of the district, located within 10 km of the inter-state border, they said.
Sub-divisional officer Lukumoni Bora along with a team of Helem police visited the areas, and seized the posters, they added.
The posters claimed the land belonged to Arunachal Pradesh, and asked Assam to vacate it at the earliest.
An inquiry has been started, officials said.
The two states share a 804-km-long border, and have been engaging in discussions to resolve the boundary disputes.
An agreement was signed by Assam CM Himanta Biswa Sarma and his Arunachal Pradesh counterpart Pema Khandu on April 20 in New Delhi in the presence of Home Minister Amit Shah.
Arunachal Pradesh, which was made a Union territory in 1972, claims that several forested tracts in the plains that had traditionally belonged to hill tribal chiefs and communities were unilaterally transferred to Assam.
After Arunachal Pradesh achieved statehood in 1987, a tripartite committee was appointed which recommended that certain territories be transferred from Assam to Arunachal Pradesh. Assam contested this and the matter is in the Supreme Court.
