US President Barack Obama said on Tuesday that the United States could be India's "best partner", but urged his hosts to do more in the battle against climate change.

Speaking to an audience of mainly young people as he wrapped up a three-day visit to New Delhi, Obama said the two 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.

The speech was the finale of a visit that 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.