India is a key US ally in the region and the visit comes hot on the heels of frosty first talks between Secretary of State Antony Blinken with top Chinese officials in Alaska.

Prior to that, Austin and Blinken visited Japan and South Korea, two other important partners in the Asia-Pacific region where China's growing assertiveness has alarmed its neighbours.

The two also attended a virtual summit between leaders of the so-called "Quad", which groups the United States, Australia, Japan and India and is seen as a check on China's ambitions.

The two-day visit to New Delhi will see Austin meet Prime Minister Narendra Modi, a senior US official said, as well as Foreign Minister S. Jaishankar, Defence Minister Rajnath Singh and Ajit Doval, a national security adviser.

- Trump ties -

US-Indian relations have long been prickly but shared misgivings about China pushed them closer together under Modi and US President Joe Biden's predecessor Donald Trump.

Twenty Indian soldiers and four Chinese troops were killed in June 2020 in a clash on their disputed border in the Himalayas, the first combat fatalities there in decades.

The Asian giants then sent thousands of extra troops to the frontier although tensions have eased in recent months with an agreement to pull back from one area of contention.

Beijing has irked New Delhi with its support for arch-rival Pakistan, as have Chinese investments in Indian Ocean nations such as Sri Lanka, the Maldives and Nepal.

India and China have also engaged in a tussle of "vaccine diplomacy", competing to supply other countries with coronavirus shots to secure goodwill and influence.

- 'Major Defense Partner' -

In 2016, the United States designated India as a "Major Defense Partner", and they have since signed a string of deals easing the transfer of advanced weaponry and deepening military cooperation.

US defence firms have inked billions of dollars in deals to supply military hardware, including helicopters, under India's $250-billion modernisation of its armed forces.

But Russia remains India's biggest armaments supplier and Modi agreed in 2018 with President Vladimir Putin a $5.4-billion deal to buy Moscow's S-400 missile defence system.

The deal falls foul of a US embargo on sales of Russian arms and India has been negotiating for years to avert sanctions, as happened with NATO ally Turkey when it ordered the S-400.

"The partnership is based on shared strategic interests that we have with India, and support and cooperation that we have together to reinforce the rules-based international order," the senior US defence official said.

But Austin may also raise the question of human rights in India, with the official calling the issue "an important part of the Biden administration defense and foreign policy".

The fact that Austin's visit comes so soon after Biden taking office "shows the priority Washington is assigning to New Delhi," Manoj Joshi from India's Observer Research Foundation said.

"Our relationship with the US on the military side has enhanced enormously and the US has been helping us in our confrontation with China," Joshi told AFP.