"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 Outlook weekly.

Karat said the Left would also launch a countrywide campaign against the party asking people to defeat the Congress in the next elections for compromising with national integrity and livelihoods of people. "We will link this to inflation and rising prices."

The top CPIM) leader 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 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.

When asked whether the Left now stand 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," he said.

"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," Karat said.