GANDHINAGAR, India (AFP) - The United States ended a decade-long boycott on Thursday of Indian opposition leader Narendra Modi over deadly religious riots as a top diplomat held talks with the man tipped to be the country's next prime minister.

Nancy Powell, the US ambassador to India, shook hands with Modi who presented her with a bouquet of roses at his official residence in western Gujarat state where he is chief minister, before entering closed-door talks.

Powell and her entourage later left Modi's residence in the state capital Gandhinagar, after the meeting lasting almost an hour, but she did not speak to waiting reporters.

Modi, leader of the Hindu nationalist Bharatiya Janata Party (BJP), is accused by rights groups of turning a blind eye to riots that killed up to 2,000 people in Guarajat in 2002. Most of the victims were Muslims.

The United States in 2005 revoked a visa for Modi under a domestic law that bars entry to any foreign official seen as responsible for "severe violations of religious freedom".

Modi has denied any wrongdoing over the 2002 violence and investigations have cleared him of personal blame, although one of his former ministers was jailed for life for instigating the killing of 97 Muslims.

Powell's meeting with Modi puts the US in line with European nations and Australia, which have already restored ties with him, as opinion polls show Modi on course to win power at general elections in May.

Modi has sought to portray himself as a business-savvy leader who can champion India's economy and tackle corruption after a decade of rule by the left-leaning Congress party.

US automaker Ford is due to open a production plant this year in Gujarat, where Modi is praised for running an efficient, pro-business government, while General Motors already has a facility there.

The United States and India have built a growing relationship since estrangement in the Cold War, with most US lawmakers supportive of ties with New Delhi.

But Modi has faced opposition from an unlikely mix of left-leaning members of the US Congress active on human rights.

If elected prime minister, Modi would be highly unlikely to experience hassles with travel to the United States, which generally allows visits by leaders of friendly countries.

A US congressional aide said this week that a meeting with Powell would send a signal of US openness on issuing a visa - an issue on which the US has little way of changing course unless Modi again applies to travel to the United States.

"A meeting with the ambassador could be a way of signalling, 'You'll get a visa,' without having to say it, which she can't," the aide said on condition of anonymity.

Concerns over personal treatment are not new to the US-India relationship.

In December, the two countries went through one of their worst crises in years when US authorities arrested a New York-based Indian diplomat on charges of underpaying her servant.

Indian lawmakers and commentators accused US authorities of humiliating the diplomat through a strip-search.

The row abated a month ago when the diplomat, Devyani Khobragade, was allowed to return to India just as she was indicted.