The Congress general secretary told reporters that he was speaking in his "personal capacity" and was pitching for the coming together of those who had parted ways with the party as the fight now was against "communal and fascistic forces".
"Those who believe in the ideology of Mahatama Gandhi and Jawaharlal Nehru must come together. The fight is against communal and fascist forces," Singh said when asked whether he thinks that leaders and parties who had parted ways with Congress should come back to join it.
He said that veteran socialist Ram Manohar Lohia had left Congress for "personal reasons" and not because of ideological differences.
A senior party functionary said he had approached NCP chief Sharad Pawar in 2009 asking him to return to the Congress fold.
Pawar's NCP in Maharashtra, West Bengal Chief Minister Mamata Banerjee's party Trinamool Congress in West Bengal, YSR Congress of Jaganmohan Reddy in Andhra Pradesh and GK Vasan's Tamil Maanila Congress in Tamil Nadu were once part of Congress.