The United States and India meet on Wednesday in their latest bid to ramp up defence and political ties, but concerns over minority rights in the south Asian giant could mar the celebratory mood.

Secretary of State Mike Pompeo and Defense Secretary Mark Esper will hold a day of talks in Washington with their counterparts from India, one of only three countries to enjoy annual so-called "2+2" talks with the United States — a format meant to encourage deep, strategic relations.

The talks come as Prime Minister Narendra Modi, bolstered by a convincing election win earlier this year, increasingly looks to solidify ties between the world's two largest democracies.

But India has been facing significant criticism for the first time since the Cold War rivals began building relations two decades ago as Modi pushes ahead with his Hindu nationalist agenda.

"We are working together more closely than many thought possible only a few years ago," said Alice Wells, the top US diplomat for South Asia.

The United States will seek ways with Indian Foreign Minister Subrahmanyam Jaishankar and Defense Minister Rajnath Singh to boost cooperation on peacekeeping, judicial training, space and science, Wells said.

The 2+2 talks — the second such meeting after last year's inaugural edition in New Delhi — is also expected to showcase India's growing defense purchases from the United States.

The two sides could formally sign a deal for India to spend more than $2 billion for 24 Romeo helicopters, which are designed to knock out submarines and ships.

The talks reflect "what has been a very strong bipartisan consensus of successive administrations on the importance of this strategic partnership," Wells said.

Unrest in India

India has nevertheless come under the microscope in Washington in recent months.

At least six people have died in major protests in the country over a citizenship law promoted by Modi that fast-tracks citizenship only to non-Muslims from neighbouring countries.

Modi says the measure is meant to protect persecuted minorities, but critics see it as part of a masterplan to define India as a Hindu nation and move away from its secular foundations.

India will likely watch closely whether and how vocally the United States raises the issue at a joint news conference.

The State Department has urged New Delhi to "protect the rights of its religious minorities in keeping with India's constitution and democratic values".

But observers in both countries say that the US administration is in an awkward position to raise concerns, considering President Donald Trump himself has called for the exclusion of Muslims and cast Mexican immigrants as criminals.

Criticism has been harsher from other parts of the US government, especially the US Commission on International Religious Freedom, which has called for the consideration of sanctions on Indian Home Minister Amit Shah over the new law.

The US Congress is also considering a bill that would press India to end all communications restrictions in occupied Kashmir and release hundreds taken into detention after Modi in August stripped Kashmiris of the special autonomy they had for seven decades by repealing Article 370 of the constitution.

While not triggering the same kinds of street protests, trade has also emerged as a sticking point in relations.

The nationalist-minded Trump earlier this year removed India from a trade preference pact under which it exported $5.6 billion in goods in 2017 — unwelcome news for Delhi as economic growth slows down.

The United States and India could also see frank exchanges on Afghanistan, from which Trump is hoping to pull out thousands of troops and end America's longest war through negotiations with the Taliban.

India is one of the most enthusiastic backers of Afghanistan's internationally recognised government and has contributed $3 billion since 2001.

But the talks on the whole may also be overshadowed. As the four ministers meet, the House of Representatives is expected to vote to impeach Trump