Sinha's comments came a day after Modi said Congress leaders met the Pakistani High Commissioner here.
"Sir! Just to win elections anyhow, and that too at the fag end of the process, is it a must to come up with and endorse new, unsubstantiated and unbelievable stories everyday against political opponents?
"Now linking them to Pakistan High Commissioner and Generals?! Incredible!" Sinha said in a tweet.
Modi on Sunday had accused a group of Congress leaders of meeting the Pakistan High Commissioner at Mani Shankar Aiyar's residence before the latter called him (Modi) "neech".
Addressing an election rally at Sanand, Modi said the meeting at Aiyar's residence was also attended by former Indian Vice President Hamid Ansari and former Prime Minister Manmohan Singh.
Continuing his attack on the Congress, Modi said: "There was a meeting convened at Aiyar's residence where Pakistan's High Commissioner, Pakistan's Foreign Minister, Ansari and Manmohan Singh were present. The meeting lasted three hours."
"The next day Mani Shankar said I am a 'neech'," said the Prime Minister. Aiyar was promptly suspended from the Congress' primary membership. He also apologised for his comment.
Sinha also advised the Prime Minister to stop communalising the atmosphere and return to the promises that the Bharatiya Janata Party (BJP) made in the 2014 general elections.
"Sir! Instead of new twists and turns, stories and cover ups, let's go straight to the promises that we made, regarding housing, development, employment of youth, health, "Vikas model".
"Lets stop communalising the atmosphere and go back to healthy politics and healthy elections. Jai Hind!," the BJP MP from Patna Sahib said in another tweet.
Sinha, a former union minister has been vocal against the policies of the Modi government, especially demonetisation and the Goods and Services Tax.