Addressing a press conference, he said the Congress would get more seats, so there is no question of backing a Left government.
"At worst, the Congress will emerge as the single largest party," he said.
Sounding confident of winning over angry allies, he said, "The UPA will form the next government... politics is the art of possible."
When asked about whether he would appeal to the Left to support UPA Government, he said, "I always believe that all secular forces have an obligation to work together to give the country a purposeful, secular government."
His statement came as the Left announced that West Bengal Chief Minister Buddhadeb Bhattacharya and Politburo member Sitaram Yachuri would engage the Left in preliminary talks on government formation after May 16.
When asked whether the Indo-US civil nuclear deal could be a sticky issue on forging ties with the Left, he said, "I think it is not an issue now. It has been signed, sealed and operationalised. It cannot be an issue for dialogue."
Attacking the NDA and the Third Front, he said the former is a fractured alliance while the latter has collapsed even before polls.
Speaking on Bihar Chief Minister Nitish Kumar, Dr. Singh said Kumar's secular credentials are in doubt after he met Gujarat Chief Minister Narendra Modi at an election rally here on Sunday. He further added that Modi's speech was a glimpse of the BJP if it came to power.
Commenting on the 1984 anti-Sikh riots, Dr Singh said his government had increased compensation paid to victims of the riots.