"I congratulate Narendra Modiji and BJP for their electoral victory. People of India have decided that Narendra Modi will be the PM again and I fully respect that," Gandhi said. He said he accepts the people's verdict and congratulated the winners. "I take 100 per cent responsibility for this defeat," he told reporters.
"Our candidates fought with whole of heart and courage. I want to thank them from my heart. Our fight is that of an ideology. There are two different set of thinkings, one is that of Narendra Modi and BJP, and the other one is Congress... We would have to accept that in this election, BJP and Narendra Modi have won," he added.
The Congress could manage to add only a few seats to its 2014 tally of 44 seats.
Gandhi has conceded defeat in Amethi, a traditional bastion of his family, to BJP's Smriti Irani but won from the second seat he contested in Kerala's Wayanad.
"I accept the verdict of the people of India. Congratulations to the winners, Mr Modi and the NDA. Thank you to the people of Wayanad for electing me as your MP. Thank you also to the people of Amethi. Thank you Congress workers and leaders for your hard work in this campaign," Gandhi tweeted later.
Asked if he would step down as the Congress president, Gandhi said, "We will have a meeting of the Working Committee. And they will decide that there."
Asked again whether he would offer to resign, he replied, "That you can leave between me and the Working Committee."
"Frankly today, with all due respect, is the day of the mandate and I don't want to colour the decision of the people of India by getting into a long conversation with you about what I think, went wrong.
"Frankly today, it doesn't matter what I think went wrong, what matter is that the people of India have decided that Shri Narendra Modi is going to be prime minister and as an Indian, I fully respect people's verdict," he said.
"I want to say that today is not the day for me to go into the details of this mandate. Today is the day that a new prime minister has been elected and today is the day to wish him all the best and, hopefully, he will look after the interests of this country," he said.
Gandhi said Congress will continue to fight the ideological battle with BJP and asked his party workers and leaders to not be afraid.
Gandhi also congratulated Irani, his rival in Amethi constituency in Uttar Pradesh, on her victory. The Congress president had won three consecutive terms since 2004.
"On Amethi results, I would like to say that Smriti Irani has won... Amethi's people have taken a decision and I respect it. This is democracy. I would like that Smriti Iraniji would take care of Amethi with love and I hope that she will reward the trust that Amethi's people have placed in her," he said.
Gandhi said there are a lot of people who believe in Congress's ideology and he would like to assure them there is nothing to worry. "I had said during the campaign that whatever you say to me or whatever you say to abuse me, I will be responding with love. And I would like to say that whatever may happen now, I will be responding with love only. This is my philosophy," he added.
"I had said that during the campaign 'janta maalik hai' and today people have clearly given their decision. I congratulate Narendra Modiji and BJP for their electoral victory," Gandhi said in a press conference he addressed at party headquarters in the national capital.
"Frankly, today is the not the day to discuss what I think went wrong because people of India have clearly decided that Narendra Modi is going to be their Prime Minister and as an Indian, I respect that," the Congress chief said.
"The Congress will continue to fight its ideological battle with BJP unitedly," he added, asking the party workers not be afraid.
Taking responsibility of his party's debacle in this Lok Sabha elections, Gandhi has also offered to resign as the Congress chief, sources said.
Riding on a massive Modi wave sweeping through most parts of the country, the BJP was set to return to power as it led in over 300 seats while the Congress trailed far behind with 52, according to trends released by the Election Commission for all 542 seats that went to polls.
If the trends translated into final results, the BJP would have improved on its 2014 performance when it had won 282 seats on its own. Adding the seats won by its allies, the BJP-led National Democratic Alliance could win 345 seats, up from 336 in 2014.
The saffron tsunami- powered by Prime Minister Narendra Modi's charisma, his planks of nationalism and development, and the BJP's organisational heft-rolled on in the Hindi heartland once more and even the apparently formidable SP-BSP combine has been blown away.
In reality, the BJP has bettered its show this time as its vote share in several states, including Madhya Pradesh, Chhattisgarh, Rajasthan, Gujarat and Haryana, is well over 50 per cent, nothing short of a statistical wonder in Indian electoral history.
(With inputs from PTI)