Indian President Ram Nath Kovind has signed the controversial Citizenship Amendment Bill (CAB), officials said Friday.

"The president has given his assent to the CAB and thus it has become an Act," an official said. "The collected set of rules in the CAB comes into effect with its publication in the official gazette on Thursday."

The CAB has been passed by both houses of Indian parliament this week. It is aimed at granting citizenship to illegal immigrants belonging to six religions - Hinduism, Sikhism, Buddhism, Jainism, Parsi and Christianity - from Bangladesh, Afghanistan and Pakistan. However, it has kept out Muslim immigrants from applying for citizenship.

With this new law, the Indian government will grant Indian citizenship to those non-Muslim immigrants who entered the country illegally before Dec. 31, 2014.

Opposition parties and civil society members criticize the bill as contrary to secular principles enshrined in India's constitution as it excludes Muslims.

The new law has triggered widespread protests in India, especially in the northeastern states of Assam and Tripura, where locals fear the immigrants would endanger their position.

On Thursday evening, two people were killed and several others injured in police firing on protesters in Assam.