NEW DELHI (AFP) ― President Barack Obama said the United States could be India’s “best partner” Tuesday but urged his hosts to do more in the battle against climate change as he wrapped up a three-day visit to New Delhi.

Speaking to an audience of mainly young people, the U.S. president said their countries could forge “one of the defining partnerships of this century” but warned the war against climate change would not “stand a chance” without India and also fired a warning about religious tolerance.

The speech was the finale of a packed visit which has seen a dramatic upturn in an often troubled relationship, including the signing of a new “friendship” pact between Obama and Prime Minister Narendra Modi.

The right-wing premier was a pariah in Washington less than a year ago but has developed a close bond with Obama, with their two countries keen to counter-balance the rise of China.

“India and the United States are not just natural partners ― I believe that America can be India’s best partner,” said Obama after receiving a rapturous welcome from a group of around 1,500 people.

“Of course, only Indians can decide India’s role in the world. But I’m here because I am absolutely convinced that both our peoples will have more jobs and opportunity, our nations will be more secure, and the world will be a safer and more just place when our two democracies stand together.”

Both Obama and Modi have been at pains to demonstrate their personal rapport during the visit and announced a breakthrough on a long-stalled nuclear power deal on Sunday.

Obama was also chief guest at Monday’s Republic Day parade ― one of the biggest honors that India can bestow on a foreign leader.

The U.S. is looking to reinvigorate alliances in the Asia-Pacific as part of Obama’s “pivot” east, and has taken note of Modi’s more assertive stance towards China.

Beijing claims sovereignty over large swathes of the South China Sea, home to maritime lanes that are vital to global trade, and is engaged in territorial disputes with a host of nations in the region.

But in his speech, Obama said “the freedom of navigation must be upheld and disputes must be resolved peacefully.”

Speaking after their talks on Sunday, Modi said he would not be pressured on climate by any country ― comments seen in part as aimed at China after it agreed on new carbon emissions targets with the U.S.

But Obama warned the battle against climate change was doomed unless developing countries reduce dependence on fossil fuels.