Twenty-five people have died in protests around India against a proposed new citizenship law seen by many as an attack on a secular constitution and against minority Muslims.
Indian police have been accused of using "unnecessary lethal force" against demonstrators who are protesting a controversial new citizenship law.
Twenty-five people have been killed around India since the law was passed earlier this month, which gives persecuted minorities from neighbouring countries an easier path to citizenship, but not if they are Muslim.
On Tuesday, Human Rights Watch called the Citizenship Amendment Act "a law that discriminates against Muslims" and demanded Indian authorities allow peaceful protests.
"Police have used excessive force only against demonstrators protesting the law, including many students ... Most of those killed have been Muslims," the group said in a statement.
"The authorities have also used a colonial-era law, internet shutdowns and limits on public transportation to prevent peaceful anti-citizenship law protests," it said.
"The police have, however, not interfered with demonstrators supporting the law, including ruling party leaders who have advocated violence."
Human Rights Watch provided media with quotes from one activist who asked not to be named.
"Many of us have gone into hiding because the police are tracking down anyone that organised or passed the word to join peaceful protest rallies ... They want to crush us into silence," the activist said.
Many police have also been injured in the protests.
South Asia director at Human Rights Watch Meenakshi Ganguly said, "the authorities should prosecute violent protesters, but they also need to hold police officers to account for using excessive force".
"The often violent repression of those critical of government undermines any claims that the authorities are responding to the situation in an impartial manner."
Critics say the law is part of Prime Minister Narendra Modi's Hindu-nationalist agenda and is "anti-Muslim", a claim his Bharatiya Janata Party (BJP) denies.
Most of India's 1.3 billion people are Hindu, about 14 per cent are Muslim and the rest are Christians, Buddhists and others.
Since being re-elected this year Mr Modi and his party have stripped Muslim-majority Kashmir of its autonomy and carried out a register of citizens in Assam, a state with a large Muslim population.
The BJP has also said it wants to conduct the National Register of Citizens (NRC) nationwide, fuelling fears that Muslims were being disenfranchised.
On the weekend, Mr Modi said, "Muslims who are sons of the soil and whose ancestors are the children of mother India need not to worry".
BJP's general secretary Bhupender Yadav told reporters Saturday that the party would "launch an awareness campaign" and hold 1,000 rallies to dispel "lies" about the law.
Additional reporting: AAP, AFP