It said Modi should at least clarify his remark which he allegedly used to "win" the Gujarat election, saying had it been Atal Behari Vajpayee as prime minister, he could have apologised 10 times.
The party also alleged that Modi was trying to break the country and blemish the image of his predecessor. It earlier demanded an apology from the prime minister.
"The prime minister is trying to break the country and blemish the image of good peple," senior Congress leader Mallikarjun Kharge told reporters outside Parliament.
He said if the prime minister had information about a "secret meeting" between senior Congress leaders and the Pakistan envoy and its ex- foreign minister which was "anti- national", then why did he not use the Intelligence Bureau and other agencies at his disposal.
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"If the prime minister had proof, why did he not take the services of intelligence agencies if there was something anti-national. He has thereby violated the oath of secrecy he has taken...If it was not in the nation's interest and was anti-national, then you have violated the Constitution and the 'maryada' (dignity) of office," he alleged.
The Leader of Opposition in the Rajya Sabha Ghulam Nabi Azad said opposition parties have demanded that the prime minister clarifies the serious allegation he made during the Gujarat election about a "secret" meeting between the Pakistan envoy and an ex-foreign minister and Manmohan Singh, former vice president Hamid Ansari and an ex-Indian Army chief.
"If he has a problem in seeking an apology, then the prime minister should say that to win the Gujarat election he threw a stunt, a "gola" (ball). It is acceptable to us," he said.
Azad said had Vajpayee been there (as prime minister), "he would have apologised 10 times. It depends on who is the prime minister".
"If the prime minister is taking his words back, we will accept that too. Then he need not apologise. He should only say that he said it to win the Gujarat election," he said.
"Let the prime minister say and admit that his job is done and now the BJP has won the election, hence I take back my words. We will accept that. The one who has levelled allegations, should explain. If there is truth in his allegations, the people concerned be punished. We are ready for it," he said.
"It is the culture of the BJP to abuse, call people anti-national, beat them, fire bullets at them. This has become an order of the day," he alleged.