Mumbai Police on Saturday received a message threatening to kill Prime Minister Narendra Modi, an official said.
The number from which the message was sent was traced to Ajmer in Rajasthan and a police team was sent there immediately to nab the suspect, said an official.
The WhatsApp message, received on the helpline of the traffic police in the early hours, mentioned two ISI agents and a plot to carry out a bomb blast to target Modi, he said.
The investigators suspect that the sender is a mentally disturbed person or was under the influence of alcohol but further probe was on, the official added.
A first information report was registered under the relevant Bharatiya Nyaya Sanhita sections.
The helpline of the Mumbai traffic police has received hoax threat messages many times in the past.