Indian Prime Minister Narendra Modi said he wants to press ahead with a national common civil code of law, a proposal bitterly opposed by Muslim activists as an attack on their faith.

India's 1.4 billion people are subject to a common criminal law but rules vary on personal matters such as marriage, divorce and inheritance.

The proposed civil code is expected to standardise laws across all religious communities but has been bitterly opposed by Muslim activists and liberals as an attack on the largest religious minority.

However, the Hindu nationalist leader said during an annual Independence Day address that the different laws divided the nation.

Modi said the laws that divide the country on the basis of religion, that become reason for inequality, should have no place in a modern society. 

He told the thousands of students, soldiers and foreign dignitaries in the audience that citizens should come out with their opinion.

The Prime Minister made this known at New Delhi's imposing 17th-century Red Fort to mark India's independence from Britain, an annual tradition since India's first prime minister, Jawaharlal Nehru, took office.

He also called for swift punishment after the horrific rape and murder of a 31-year-old doctor in a hospital in Kolkata last week, a killing that has triggered widespread demonstrations and a strike by fellow doctors.

Modi won a third successive term in office in June but was forced into a coalition government after a shock election setback for his Bharatiya Janata Party left him without an outright majority for the first time in a decade.