A bill that would grant citizenship to non-Muslims who migrated illegally from Pakistan, Bangladesh and Afghanistan was approved by India's lawmakers on Wednesday.

Known as the Citizenship Amendment Bill, it grants Indian nationality to Buddhists, Christians, Hindus, Jains, Sikhs and Parsis who came to the country before 2015 from those three neighboring countries. However, it has kept out Muslims from applying for the citizenship.

It won a slim majority in India's upper house in a 125-105 vote on Wednesday.

The bill was introduced in the house by Home Minister Amit Shah, who vehemently countered the opposition's claims that the bill was an assault on the constitution of India.

Opposition parties criticized the bill as contrary to secular principles enshrined in India's constitution and discriminatory as it excludes Muslims.

"Today marks the dark day in the constitutional history of India. The passage of the Citizenship Amendment Bill marks the victory of narrow-minded and bigoted forces over India's pluralism," Congress Party chairperson Sonia Gandhi said.

The bill has already triggered widespread protests in the country especially in the northeastern states of Assam and Tripura, bordering Bangladesh, as locals fear non-Muslim immigrants will endanger their position.

The bill needs to be signed by the country's ceremonial president before it becomes a law. Several opposition lawmakers say the bill will be challenged in court.

(With input from agencies)