Indian police are "harassing" primary school students by repeatedly questioning them after their school was charged with sedition over a play allegedly criticising the government's contentious citizenship law, rights groups said Wednesday.

India has been gripped by widespread street demonstrations against the law that grants citizenship to religious groups from three neighbouring countries, but excludes Muslims.

Police questioned nearly a dozen young student actors after a member of the youth wing of Prime Minister Narendra Modi's Hindu-nationalist Bharatiya Janata Party filed a complaint against the school in Bidar district in southern Karnataka state.

A teacher and a mother of an 11-year-old participant were arrested under the British colonial-era law for helping the children with the performance, which was part of the school's foundation day programme. "They have been asked to explain the reasons over repeated questioning of children," the head of the Karnataka State Commission for Protection of Child Rights, Anthony Sebastian, told AFP.

CCTV footage released by the school showed one policeman questioning students as another officer recorded the interviews on a camera. Other videos showed children in uniform being led by plain-clothes policemen to a room, where they were quizzed.

The play depicted a worried family talking about how they feared the government would ask millions of Muslims to prove their nationality or be expelled from India. The citizenship law, combined with a mooted national register of citizens, has stoked fears that India's 200 million Muslims will be marginalised.

The play ended with a poem written by a Bollywood lyricist that has become a rallying point for hundreds of thousands of protesters across India.

Amnesty International India urged the government to drop the sedition charges. "It is shameful that the Bidar police have been harassing and intimidating the school children by repeatedly interrogating them over their involvement in the school play," executive director Avinash Kumar said in a statement.

Bidar police chief T. Sreedhara told AFP his men were "following the rules while questioning the students". "The investigation is still on," he added.

The British-era sedition law enacted in 1860 carries a maximum penalty of life in prison. Prosecutions are rare but it has frequently been used against critics of the government of the day.

Activists say the authorities often misuse the law to stifle dissent. India's junior home minister on Wednesday told the parliament that more than 230 people were charged with sedition between 2014 and 2018.