"As far as this issue is concerned, the decision was taken by the party. It was not a normal decision. It could not be taken without any reason behind it " Swaraj told media.
"I can say I am personally pained by this decision," she said.
Upset with his party for being denied the Barmer seat in Rajasthan to contest the Lok Sabha polls, Jaswant Singh on Saturday said there has been encroachment on the principles and ideologies of the party.
"There has been encroachment on the principles and ideologies of the BJP. I don't understand on what principles the BJP is leading and where the course of the party is going," he told NDTV.
An emotional Singh told the channel: "My honour cannot be subject to trading."
Singh is also likely to quit the party and contest the polls as an Independent candidate from Barmer in Rajasthan, said reports on Saturday.
Singh's supporters on Saturday burnt effigies of the party's prime ministerial candidate Narendra Modi, a day after he was denied ticket from Barmer.
The BJP on Friday denied the Barmer seat to Singh, who wanted to contest the Lok Sabha elections from the constituency.
The BJP, in its sixth list of candidates, has instead given the ticket to Colonel Sonaram Choudhary .
Singh had reportedly told the BJP leadership that he wanted to contest from the Barmer constituency in Rajasthan.
He has been fielded from Dahod in Gujarat.
The BJP on Friday released the sixth list of candidates.