"Congress has always formed government at the Centre without the support of Left parties. In 2004, they themselves came forward to support the Congress-led UPA to stop the BJP and save their existence," Mukherjee said in a poll rally at Parul village near Bhatar in Burdwan district.

He said the Left parties were not a political force in the national arena and do not exist outside the three states of West Bengal, Kerala and Tripura.

Mukherjee said at another election rally at Arambagh in Hooghly district that he saw no chance of the Third Front coming to power at the Centre as indicated by the voting trends.

In two of the three CPM-ruled states -- Kerala and Tripura -- the voting trends indicated that the Third Front was not able to take off, Mukherjee told election meetings in Hooghly and Burdwan districts.

After the results come out, it would be proved that the Third Front was not at all a viable political alternative and was merely an imaginary thing, he said.

"How can it aspire to come to power at the Centre when it did not even put up candidates in 272 seats which is the magic number and failed to decide on a prime ministerial candidate?" Pranab Mukherjee asked.

He also took a dig at the Third Front, saying that the CPM was dreaming of forming a government at the Centre without having a prime ministerial candidate.

"We have decided on Manmohan Singh as the prime ministerial candidate. The NDA has L K Advani. Who will be the PM of the Third Front?" he asked.

He said the Left parties withdrew support to the UPA government on the issue of Indo-US nuclear deal, which he felt, would meet the power crisis at a time when the state is reeling under daily power cuts.

"Thirty crore people in our country are living without electricity. Where will so much power be generated without nuclear energy? We have not sold ourselves to any country. France, Russia, the UK, the US are all coming forward to sign deals," he said.