Indian police have detained hundreds who defied a ban on protests against a controversial new citizenship law. The ban has been imposed in parts of the capital Delhi, and throughout the states of Uttar Pradesh and Karnataka. Mobile data services are suspended in some parts of Delhi close to protest sites. There have been days of protests across India, some violent. The new law offers citizenship to non-Muslim illegal immigrants from Pakistan, Bangladesh and Afghanistan. Among those detained are Ramachandra Guha, a prominent historian and outspoken critic of the government, in the southern city of Bangalore; and political activist in Yogendra Yadav in Delhi. The law - known as the Citizenship Amendment Act (CAA) - has sharply divided opinions in India. The federal government, led by the Hindu nationalist Bharatiya Janata Party (BJP), says it will protect people from persecution, but critics say it's part of a "Hindu nationalist" agenda to marginalise India's more than 200 million Muslims. The police chief of Uttar Pradesh, OP Singh, has asked people to stay away from protests. The police order, based on a severely restrictive law, prohibits more than four people from gathering in a place. Officials say the ban has been imposed to avoid violence. Police in other places - such as Chennai (formerly Madras) - have denied permission for marches, rallies or any other demonstration. But the protests have been continuing in Uttar Pradesh, Bangalore, Hyderabad, Patna, Chandigarh, Mumbai, Delhi and other cities - civil society groups, political parties, students, activists and ordinary citizens took to social media platforms such as Instagram and Twitter, asking people to turn up and protest peacefully. Police also put up barricades on a major highway connecting Delhi and the city of Jaipur and are checking all vehicles entering the capital. This has led to massive gridlock and many commuters have missed their flights. A number of metro stations in Delhi have also been shut.