Police in India have detained two men suspected of killing an activist who campaigned against superstition and "religious charlatanism" - a killing that shocked the nation and led hundreds of self-proclaimed rationalists to protest in the western city of Pune.

The suspects, both from Mumbai, were detained for allegedly firing four shots at Narendra Dabholkar, 68, in Pune on August 20.

Police tracked the suspects, said to be in their 20s, down to the seaside resort state of Goa and arrested them.