Arvind Kejriwal, the leader of Aam Admi (Common Man) Party, was stopped and briefly held by police as he embarked on a four-day tour of the western Indian state of Gujarat.
After being allowed to walk free, Kejriwal - who quit as the Delhi chief minister last month following a short stint in office - said on Wednesday his brief detention was an attempt by the Bharatiya Janata Party's prime ministerial candidate, Narendra Modi, to harass him "as we are exposing all claims of development and good governance".
Modi, the current chief minister of Gujarat, is seeking to woo voters across the country by publicising development and good governance that he claims to have given his home state.
According to the Indian Express newspaper, senior police officials questioned Kejriwal about whether he had the necessary permission for his road show. Kejriwal intends to travel across the state to see for himself what Modi has done for Gujarat.
After a rousing welcome at the Ahmedabad airport, he headed for Echchwada village, near Hansalpur where a car-manufacturing plant is being built, to listen to farmers' concerns.
Farmers of the region had opposed the government's acquisition of their land to set up industry.
The AAP was born out of an anti-graft campaign that swept the nation about two years ago. It made a stunning electoral debut in New Delhi and formed the government after Congress supported it. Kejriwal, however, quit a few weeks later after he was not allowed to pass a strong anti-corruption bill.
The party has shaken up India's mainstream political parties with its tough stance on corruption and immorality.