"Mani Shankar Aiyar is mentally unfit," the former union minister said.
Aiyar earlier today called Modi a "neech aadmi" (vile man) who does "dirty politics" after the prime minister targeted the Congress saying that parties seeking votes in B R Ambedkar's name tried to erase his contribution to nation building the party.
Expressing his thoughts on Twitter, Gandhi said that it is not the Congress party's culture to use such language against political opponents.
Soon after Congress vice president lashed out at Aiyar for calling the Prime Minister 'neech', the veteran leader came out with a clarification.
In his defence, Aiyar said "I meant low level when I said 'neech', I think in English when I speak in Hindi as Hindi is not my mother tongue. So if it has some other meaning then I apologise."
Asked about Rahul Gandhi`s tweet that he did not appreciate Aiyar`s words to address the Prime Minister, Aiyar said he could talk about it only after meeting Gandhi.
PM Modi attacked Congress leader Aiyar for calling him a "neech jaati" (low caste) man and said by this he has insulted all the Gujaratis who will give a befitting reply to the Congress by voting for the BJP in the upcoming assembly elections.
"They can call me `neech jaati`. Yes, I am from the poor section of society and will spend every moment of my life to work for the poor, Dalits, tribals and backward classes. That is my culture. They can keep their language, we will do our work," Modi told an election rally in Gujarat.