An aide to Bharatiya Janata Party (BJP) candidate Smriti Irani, who recently defeated Congress party chief Rahul Gandhi for a seat in parliament, was shot dead overnight, police said on Sunday.

Surendra Singh was an aide to Irani, a former television actress and dogged minister in Prime Minister Narendra Modi's cabinet.

In one of the biggest upsets of the election that handed the BJP a second term, Irani beat Gandhi in the Amethi constituency, which had been held by his family almost continuously for the last four decades, in Uttar Pradesh.

Singh worked closely with Irani and distributed sweets and paraded with celebrating supporters on Friday, a day after the election results, his relatives told Reuters partner ANI.

He had gone to sleep on the veranda outside his home when unidentified gunmen shot him, Amethi Superintendent of Police Rajesh Kumar told Reuters on Sunday.

"Some unknown people have fired on him and he died due to firearm injury," Kumar said.

Seven people have been arrested, Kumar said, adding it was too early to draw conclusions about a motive.

Requests for comment from two BJP spokesmen went unanswered. An official at the BJP headquarters in Uttar Pradesh was unable to immediately provide any information.