NEW DELHI: India''s coalition government was undergoing a major shake-up Friday with the dominant Congress party pushing on with a controversial nuclear deal with the US and ditching left-wing allies.

A four-party bloc of Communist and leftist parties met Friday to discuss what politicians described as the "modalities" of a divorce from the Congress-led government because of the pact.

The Congress party, however, was working to avoid being forced into early elections and getting the atomic deal through by negotiating a new alliance with the socialist and regional Samajwadi Party (SP).

SP leader Mulayam Singh Yadav met Prime Minister Manmohan Singh and Congress party chief Sonia Gandhi separately to finalise their agreement, officials said.

After talks with PM Singh, Yadav told reporters that "national interest is more important than politics" -- seen as a sign that a deal to reshape India''s ruling alliance was close.

Later, senior Congress leader Veerappa Moily told NDTV news channel: "We have the numbers now. Their (Samajwadi Party''s) help has been very timely."

The nuclear deal -- agreed in principle in 2005 -- would allow India to buy atomic power plants and technology despite not having signed international non-proliferation pacts. Prime Minister Singh argues the pact is crucial for India''s energy security.

Singh is lined up to meet US President George W. Bush on the sidelines of the G8 meeting in Japan next week, taken as another sign that Congress was blazing ahead with implementing the pact the two leaders agreed to in 2006.

After their meeting Friday, India''s top Marxist leader Prakash Karat set Monday as a deadline for the government to clearly declare whether it was proceeding with the deal.

"We wish to know... whether the government is proceeding to seek the approval for the safeguards agreement by the IAEA (International Atomic Energy Agency)," Karat said.

"Please let us know by July 7, 2008," Karat told reporters, adding that the Left parties would meet a day later for a final decision on withdrawing support.

The ultimatum was rejected by Congress, whose spokesman Abhishek Singhvi said "sovereign governments or political parties cannot be subjected to deadlines."

"We are happy that other parties in the national interest are slowly converging to our view point," he told reporters.

"We are working towards triple objectives -- to do a nuclear deal in national interest, to carry along our allies with us for that purpose and to go to elections as per schedule" in May 2009.