President Barack Obama and Indian Prime Minister Narendra Modi declared an era of "new trust" in the relationship between their nations as the US leader opened a three-day visit to New Delhi.

Standing side by side at the stately Hyderabad House, Mr Obama and Mr Modi cited progress toward putting in place a landmark civil nuclear agreement, as well as advances on climate change and defence ties.

But from the start, the day was more about putting their personal bond on display. Mr Modi broke with protocol and wrapped Mr Obama in an enthusiastic hug after the president got off Air Force One.

Mr Obama later told reporters that Mr Modi's "strong personal commitment to the US-India relationship gives us an opportunity to further energise these efforts."

Mr Modi was as effusive. He called Mr Obama by his first name and said "the chemistry that has brought Barack and me closer has also brought Washington and Delhi closer".

The centrepiece of Mr Obama's visit was today's annual Republic Day festivities, which got under way on a foggy, rain-soaked morning in New Delhi.

The crowd erupted in cheers as the president, along with first lady Michelle Obama, emerged from his armoured black limousine and took his seat next to Mr Modi on a viewing stand overlooking the parade route.

Republic Day marks the anniversary of India's democratic constitution coming into force.

The parade, which weaves its way past the imposing India Gate monument and a memorial to the unknown soldier, is part Soviet-style display of India's military hardware, part Macy's Thanksgiving Day-type parade with floats highlighting India's cultural diversity.

Mr Obama's presence would have been unlikely only a few years ago.

Relations between the US and India hit a low in 2013 after an Indian diplomat was arrested and strip-searched in New York over allegations that she lied on visa forms to bring her maid to the US while paying the woman a pittance.

The official's treatment caused outrage in New Delhi, and India retaliated against US diplomats.

The US and India also were at an impasse over implementing the civil nuclear agreement signed in 2008.

The US insisted on tracking fissile material it supplied to India. Also, Washington was frustrated by Indian legal liability provisions that have discouraged US companies from capitalising on new energy development in India because of concerns about their legal responsibilities in the event of a nuclear power plant accident.

Yesterday, Mr Obama said he and Mr Modi had reached a "breakthrough understanding" on those areas of disagreements. Details on an accord were sparse.

Ben Rhodes, Obama's deputy national security adviser, said only that India "moved sufficiently on these issues to give us assurances that the issues are resolved".

The president and first lady were hosted at a state dinner featuring a dance performance by a cultural group that performed during Mr Obama's 2010 visit to India.

Taking some of the lustre off the trip, Mr Obama does plan to cut his time in India slightly short.

Following a speech tomorrow morning, he will travel to Saudi Arabia to pay respects to the royal family following the death of King Abdullah.

To make the trip to Riyadh, the president scrapped plans to visit India's famed white marble Taj Mahal.

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