NEW DELHI, July 4 (Reuters) - India's communist parties said the government must tell them by Monday if it plans to press ahead with the next step in a controversial civilian nuclear deal with the United States, which they strongly oppose.

The communists have threatened to withdraw support for the government if it seeks approval for the deal from the International Atomic Energy Agency (IAEA), the next international move needed to operationalise the pact.

"We wish to know definitely whether the government is proceeding to seek the approval of the safeguards agreement by the board of governors of the IAEA," said Prakash Karat, head of the Communist Party of India (Marxist), reading out a letter addressed to the government.

"Please let us know the position by July 7, 2008."

The party said it would launch a national campaign from July 14 to explain its opposition to the nuclear deal and what it called "runaway" inflation.

The government is attempting to line up support from a regional party to provide it with a parliamentary majority and avoid early elections if the communists pull out. (Reporting by Bappa Majumdar; Editing by Alistair Scrutton and Mark Williams) (For the latest Reuters news on India see: http://in.reuters.com, for blogs see http://blogs.reuters.com/in)

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