In yet another incident of Chinese incursion, about 250 China's Peoples Liberation Army soldiers entered Arunachal Pradesh's east district of Kameng four days ago, defence sources said on Monday.
The "temporary transgression" by the Chinese patrolling party happened in Yangste, East kameng district on June 9, they said.
However, the soldiers went back within hours, they added.
Significantly, the Chinese crossing-over happened at a time when Beijing had hardened its opposition against India's bid for membership of the 48-member Nuclear Suppliers Group (NSG).
This is the first known transgression by the Chinese army this year in the region, which China claims is part of its territory.
The Chinese troops spent about three hours on this side of the border before going back to their territory, the sources said.