RAMSTEIN BASE: US Secretary of State John Kerry was due to land in India Wednesday on a mission to break the ice with new Prime Minister Narendra Modi and repair a rut in a once warming relationship.

For the past two decades, the world's two largest democracies have described themselves as natural allies, sharing similar concerns over China's rise and religious extremism.

But incidents including the US arrest of an Indian diplomat last year sent relations plunging to their lowest point in years, and the Hindu nationalist Modi had been treated as a pariah by Washington before he led his party to a decisive victory in April-May elections.

Ahead of his visit, Kerry said that Modi's strong mandate opened up new possibilities for cooperation on issues from boosting trade to fighting climate change.

“This is a potentially transformative moment in our partnership with India, and we're determined to deliver on the strategic and historic opportunities that we can create together,” Kerry said.

The top US diplomat will hold talks with Indian officials on Thursday and meet Modi on Friday, said a US official traveling with Kerry, who stopped for refuelling in Germany.

For some observers, Kerry's three-day trip is in itself a sign of India's importance. He has focused much of his tenure on crises in the Middle East, and returned just Sunday from a grueling, unsuccessful mission to end the Gaza conflict.

“It is significant that the secretary is able to stick to making time for the Strategic Dialogue with India when there are literally parts of the world in flames,” said Alyssa Ayres, a former State Department official.

Lingering resentment

Despite strong ties between their people, the Indian and US governments have frequently been at odds.

After tensions during the Cold War and US sanctions over India's 1998 nuclear tests, former president Bill Clinton began reconciliation efforts. His successor George W. Bush pushed through a landmark nuclear cooperation accord with India.

But some Indian commentators saw President Barack Obama as less interested in the relationship, even though he threw US support behind New Delhi's leading goal of winning a UN Security Council seat.

Relations took a sharp turn for the worse when US authorities in December arrested an Indian diplomat on allegations of mistreating her servant, leading New Delhi to retaliate against US personnel.

Modi has little reason for gratitude toward the United States. In 2005, Washington refused him a visa over allegations of turning a blind eye to anti-Muslim riots as leader of the state of Gujarat.

Other nations were quicker to embrace Modi, with British and French ambassadors courting him well before the election. He also traveled to Japan and China.

D.H. Pai Panandiker, head of the Indian think tank the RPG Foundation, said that the United States was seen as unresponsive by cold-shouldering Modi for so long.

And the diplomat's arrest showed that “America does not appreciate the sensitivities of India. And therefore, there is anger in India. There is a sense of resentment,” Panandiker said.

New row on WTO

Obama has invited Modi to the White House in September. Modi does not appear eager to play up grudges and instead has shown pragmatism, meeting in his first months in office with the leaders of Pakistan and China despite his past hardline stances.

But in an unexpected rift ahead of Kerry's visit, Modi's government warned it may hold up a global customs pact that must be ratified by Thursday unless the World Trade Organisation approves India's food subsidy programs.

India buys grain at inflated prices to sell at subsidised prices. The program is important for India's hundreds of millions of poor, but rich nations say that it distorts trade.

The US official travelling with Kerry voiced hope of reaching an understanding that will salvage the deal “over the next few days”.

Ayres, now a senior fellow at the Council on Foreign Relations, said that India's stance “cast a huge and very different kind of shadow” on trade issues, especially as Modi has billed himself as an economic reformer.