Barack Obama has arrived in New Delhi for an unprecedented second visit to India by a serving US president aimed at consolidating what he has called one of the "defining partnerships of the 21st century".
The US president attended on Sunday a welcome ceremony hosted by his Indian counterpart Pranab Mukherjee. He inspected the guard of honour outside the presidential residence - the Rashtrapati Bhavan, in New Delhi.
"I am grateful for the extraordinary hospitality, it's a great honour to be back in India," President Obama said.
He later visited Raj Ghat, the memorial of Mahatma Gandhi, to pay homage to the leader of India's independence struggle.
He will be the first US president to attend India's Republic Day parade, a show of military might long associated with the anti-Americanism of the Cold War, and will host a radio show with Prime Minister Narendra Modi.
Modi greeted Obama and his wife, Michelle, on the tarmac of Palam Air Force Base in New Delhi as they came down the steps from Air Force One. The Indian prime minister broke with protocol to meet and bear-hug Obama when he landed in New Delhi.
Up to 40,000 security personnel have been deployed for the visit and 15,000 new closed-circuit surveillance cameras have been installed in the capital, according to media reports.
His presence at Monday's parade at Modi's personal invitation is the latest revival in a roller-coaster relationship between the two largest democracies that just a year ago was in tatters.
"I'd like to think the stars are aligned to finally realise the vision [of] India and America as true global partners," Obama said in an interview with India Today , a weekly magazine, published on Friday.
The two sides have worked to reach agreements on climate change, taxation and defence cooperation in time for the visit. Talks on a hoped-for deal on civil nuclear trade went down to the wire with no clear solution at the weekend.
The US views India as a vast market and potential counterweight to China's assertiveness in Asia, but frequently grows frustrated with the slow pace of economic reforms and unwillingness to side with Washington in international affairs.
India would like to see a new US approach to Pakistan.
"Particularly with regards to security, and we would like a much greater understanding with the United States with regards to regional issues," India's Finance Minister Arun Jaitley said in Davos ahead of Obama's visit, Reuters news agency reported.
Elected last May, Modi has injected a new vitality into the economy and foreign relations and, to Washington's delight, begun pushing back against China's growing presence in South Asia.
Annual bilateral trade of $100bn is seen as vastly below potential and Washington wants it to grow five-fold.