"I am not a doctor to comment on his physical condition. In politics, the word impotent is used for someone who is incapable, who lacks capacity. This is about incompetence and incompetence is too soft a word to use in this context," Mr Khurshid said.
Yesterday, while addressing a gathering in his Lok Sabha constituency Farukkhabad in Uttar Pradesh, the minister said, without naming Mr Modi, "You claim to be such a strong and powerful man and wish to be the PM, and you could not protect the people of Godhra... Are you not a strong man?...Our allegation is not that you get people killed, but that you are napunsak (impotent)."
As it added to the increasingly personal attacks flying about in the build-up to the national election in three months, Rahul Gandhi seemed to have a message for Mr Khurshid.
"When politicians speak with hatred, it is going to harm you," Mr Gandhi said in an interaction at a school in Guwahati, Assam.
Mr Modi's critics say he did not do enough to stop the riots in his state 14 years ago but recently, the Supreme Court said it could find no evidence to prosecute the Chief Minister.
"It is regrettable and shameful, that too from the foreign minister of India. Mr Khurshid must apologise for the kind of language he used," said BJP leader Ravi Shankar Prasad.
Last month, Congress leader Mani Shankar Aiyar mocked Mr Modi's tea-seller past at a party conclave saying, , "There is no way he can be Prime Minister in the 21st century... but if he wants to come and distribute tea here we can make some room for him." Rahul Gandhi later cited these remarks while tell his party men to avoid personal comments.