US Secretary of State John Kerry on Sunday urged a greater role for India on Afghanistan and climate change as he sought to revive stuttering cooperation between the world's two largest democracies.

On his first visit to India as the top US diplomat, Kerry tried a few words in Hindi, pressed his hands in a traditional namaste greeting and quoted Mark Twain who said the diverse land was the sole country all people want to see.

Kerry firmly supported an involvement in Afghanistan for India, which is desperate to avoid a return of the Taliban once US troops leave but whose aid and diplomacy are viewed with suspicion by mutual neighbour Pakistan.

Kerry said that India had a "central role" in ensuring free elections due in April next year in Afghanistan. A week after a false start in US dialogue with the Taliban, Kerry acknowledged that a final settlement "may be long in coming".

"We should and must work together to support an inclusive, legitimate democratic process that helps the Afghan people unify around a new leader who will build on the economic and social gains achieved under President (Hamid) Karzai," Kerry said.

Kerry, who will meet the Indian leadership on Monday, devoted most of his speech to climate change in what his aides said was a signal that the scourge will be a top priority for him as secretary of state, much as it was when he was a senator.

"Here in India, the home of so much of the history of science, we must recognise that today the science of climate change is screaming at us for action," Kerry said.

After expressing his condolences for the victims of devastating floods in northern India, Kerry said that "it appears as if, in many ways, in many places, Mother Nature is telling us to heed the warnings".

"Yours is already one of the most severely affected nations -- and unfortunately, the worst consequences of the climate crisis will confront people who are least capable of coping with them," Kerry added.

Kerry's trip comes as critics say the US-India relationship has fallen into a funk, with ties cordial but not near the level envisioned nearly 20 years ago when the democracies began to reconcile from Cold War estrangement.

US businesses accuse India of reneging on agreements to open its economy -- an issue on which Kerry again pressed New Delhi -- while India has been suspicious of attempts in the US Congress to curb visas for high-tech workers.

Climate change is one area where the two have open disagreements, with India a leader among developing nations that resist a binding international accord on grounds that wealthy countries bear historic responsibility for the problem.

Kerry argued that action on climate change would benefit the Indian economy by addressing the growing economy's need for power.

Trying to underscore Kerry's message, the United States announced a $100 million partnership with the private sector to invest in clean energy in India. Rajiv Shah, head of the US Agency for International Development, who was accompanying Kerry, said the initiative would power tens of thousands of homes.

"Just as our two democracies offer the world a vibrant choice beyond the stale stability of autocracy and the chaos of extremism, our action on global climate change together can inspire others to see a future where environmental stewardship and economic dynamism go hand in hand," Kerry said.

Kerry, a former presidential candidate, led efforts in the US Congress to require the first nationwide restrictions on carbon emissions. The proposal died in 2010 after staunch opposition from the rival Republican Party.

His speech in New Delhi comes two days before President Barack Obama will unveil a long-awaited new plan to battle climate change.

Kerry, while mostly general in tone, called on India to wind down production of hydrofluorocarbons, which are found in air conditioners and refrigerators and are notorious for their carbon pollution.

China had long argued with India that it was unrealistic to shift away from the super greenhouse gases. But President Xi Jinping agreed on the need for a phaseout in a sign of cooperation during a June 8-9 summit with Obama.

Kerry's arrival in New Delhi was overshadowed by news that former intelligence operative Edward Snowden, who faces a US arrest warrant over his leaking of a massive surveillance programme, had flown out of Hong Kong. Officials travelling with Kerry declined comment.