KOLKATA (AFP) - Police in eastern India said Saturday they were investigating the gang-rape of a 75-year-old nun by burglars who broke into the convent school where she lived.

Two people have been arrested in connection with the alleged attack on Friday night, when 12 men broke into the convent in West Bengal state.

"A preliminary investigation has revealed that a nun at the school was gagged and gang-raped," police inspector general Anuj Sharma told AFP.

"Two people have so far been arrested," he said, adding that the nun was recovering in hospital.

Local residents took to the streets in anger, shouting slogans demanding action and blocking off the main highway.

West Bengal Chief Minister Mamata Banerjee tweeted her condemnation of what she called a "horrific attack", promising "swift, strongest action".

The incident came at a time of heightened sensitivity over women's safety in India, which last week banned a documentary about the 2012 gang-rape of a student in Delhi that sparked mass protests.

Authorities said screening the documentary could have caused public disorder, but critics accused the government of being more concerned with the country's reputation than the safety of its women.

The December 2012 gang-rape of a young physiotherapy student, who cannot be named, highlighted the frightening level of violence against women in the world's second most populous country and triggered mass protests.

It led to a major reform of India's rape laws, speeding up trials and increasing penalties, although many campaigners say little has changed for women on the ground.