Virtually reaching a point of no return on the nuclear deal, the Left parties on Friday said they would vote against the United Progressive Alliance government in Parliament in case of a confidence motion if it took the next step to operationalise the agreement.

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"If there is a vote of confidence in Parliament on the issue, the Left will vote against the government. But we will do so only after the Government formally conveys its decision to proceed with the deal," CPI-M general secretary Prakash Karat told the Outlook magazine.

His CPI counterpart A B Bardhan, in an interview to Times Now television channel, however, did not say whether they would join hands with BJP to bring down the government in case of a confidence vote but made it clear that they would pull out if it went to the International Atomic Energy Agency.

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Karat said the Left would also launch a nationwide campaign against the Congress asking people to defeat the party in the next elections for compromising with national interests.

"We will link this to inflation and rising prices."

Bardhan, on the other hand, said, 'we have sent them a letter on Friday and given them three days time that you tell us by the 7th (July). We will meet on the 8th or 9th. We will withdraw support if they give us a reply that they are going ahead, because every step is in that direction.'

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The CPI leader said then the Left parties would go to the President and 'give her the letter withdrawing support. It will bring them down to a minority.'

In the interview, Karat said his party never expected to break with the UPA on a foreign policy issue. 'We had not thought the break would come on a foreign policy issue and American imperialism at that. We thought it would be on domestic policy. But since July 2005, when Prime Minister Manmohan Singh [Images] went to Washington, it (nuclear deal) has been running thread of the conflict. Two years ago, we knew this was an issue on which we would not compromise,' Karat said.

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When asked whether the Left now stands politically-isolated with the Samajwadi Party moving closer to Congress, he said they had not expected Mulayam Singh Yadav to cross over, noting that the UNPA will now disintegrate.

'We don't like to lose allies, but we cannot be opportunistic on policy issues,' Karat asserted.

'We were never part of the UNPA. We merely cooperated with it on issues. With SP taking the position it has, the UNPA will now disintegrate,' he said.

The CPI-M leader noted that a third alternative can only emerge through agreement on a common policy framework and not through electoral compulsions or exigencies.