The U.N.'s nuclear watchdog head begins a long scheduled trip to India on Monday that has turned into a political flashpoint as a nuclear energy deal with the United States threatens to spark snap elections.

Mohamed ElBaradei, director general of the International Atomic Energy Agency (IAEA), is ostensibly on a technical visit to speak at an energy conference, visit a nuclear research facility in Mumbai and meet with Indian nuclear officials.

But the trip comes just as India faces an informal end-October deadline to begin securing clearances from the IAEA and others to clinch the nuclear energy deal -- opposed by its communist allies who say the deal would enslave New Delhi to U.S. policy.

The deal would be a milestone in India-U.S. relations, not the best of friends during the Cold War. It would allow India to import U.S. nuclear fuel and reactors, despite having tested nuclear weapons and not signed the Non-Proliferation Treaty.

Critics say the deal unfairly rewards India and undercuts a U.S.-led campaign to curtail nuclear ambitions of nations like Iran. A week before the IAEA visit, U.S. lawmakers introduced a non-binding resolution in the House of Representatives questioning if the deal complied with U.S. law.

In India, the communists have warned the government against negotiating with the IAEA to place India's civilian nuclear reactors under U.N. safeguards, one of the first steps towards making the deal operational.

But Sonia Gandhi, ruling Congress party head and India's most powerful politician, sharpened the rhetoric on Sunday in a statement widely seen as hinting she was ready for a snap vote, calling opponents of the nuclear deal enemies of development.

The IAEA says it is not a political visit.

"There is no expectation that the India-US agreement will be front and centre of his visit there," said a Vienna diplomat close to the IAEA.

"It just depends on India, when the timing is right, to make the essential approach about drafting a safeguards agreement. We don't have any indication that this is going to happen then."

But some experts say timing is everything when it comes to ElBaradei's visit and that government officials could meet with him, a move bound to anger the left.

"There is little doubt the Indian government has decided to go ahead with the deal and couldn't care less what the left has to say," R.R. Subramanian, an independent nuclear expert, said.

"So I think that they are going to talk to ElBaradei."

India's Department of Atomic Energy said he would be arriving on Monday night and that his official program would start on Tuesday.

The Vienna-based diplomat said ElBaradei could discuss the deal informally.

"I know the US considers ElBaradei's trip extremely important at this time," the diplomat said. "But for the IAEA, it's a technical matter -- we get a list of facilities first and then we start moving."

"In general there might be a discussion of where things stand. But the issue is still in a political realm and it is not for the IAEA to touch that."

The government and its communist allies formed a joint panel to end the stand-off, but so far neither side seemed to budge from their position. The panel will meet again on Tuesday.

After negotiating with the IAEA, India must get clearance from the 45-nation Nuclear Suppliers Group (NSG) that control global civilian nuclear commerce. Then the deal goes back to the U.S. Congress for a final approval.

(Additional reporting by Mark Heinrich in Vienna)