Unidentified people hurled petrol bombs at the state headquarters of the Bharatiya Janata Party (BJP) in Meghalaya late on Sunday night, a police official said on Monday.
No one was injured in the attack but the windows of the office chamber of state BJP President Shibun Lyngdoh were damaged.
The petrol bomb attack comes amid the protests against the Modi government's bid to get the controversial Citizenship (Amendment) Bill, 2016 passed in Parliament.
The Bill aims to amend the Citizenship Act, 1955, to make illegal migrants who are Hindus, Sikhs, Buddhists, Jains, Parsis and Christians from Afghanistan, Bangladesh and Pakistan eligible for citizenship of India.
"We were informed that the incident occurred at around 11.20 p.m. and a fire engine doused the flames," Superintendent of Police (Shillong City) Stephan Rynjah told IANS.
A team of forensic experts on Monday visited the BJP headquarters to collect samples and took possession of the CCTV footage capturing the incident.
BJP legislator and Health and Family Welfare Minister Alexander Laloo Hek, who visited the party office, demanded the immediate arrest of the perpetrators.
"We don't know the reason behind this cowardly attack which is totally unacceptable," Mr Hek told IANS.