Washington has been seeking to send Susan Coppedge, its newly appointed anti-people trafficking ambassador, and Randy Berry, its special envoy for LGBT rights, to New Delhi this month.

Human trafficking has caused friction between the United States and India. The countries also disagree on gay rights, which the Obama administration promotes, while homosexuality in India is illegal.

The source, who did not want to identified, said the visits had run into problems.

“These visits were planned, they were meant to be here around this time. But there were some issues," the source said.

The State Department declined formal comment but a department official said the two sides were "working to coordinate the best timing.”

India`s Foreign Ministry did not respond to request for comment and Indian Ambassador Arun K. Singh did not offer clarification when asked on Thursday about Coppedge`s plan to visit, which was revealed at a Nov. 4 congressional hearing by Kari Johnstone, principal deputy director of the State Department`s trafficking office.

"We`ll see," Singh told reporters. "When you ask a U.S. official when somebody will be given a visa, they always say ‘we will assess when visa is applied for.’ ... I can do no better than to reiterate the U.S. position."

The human trafficking issue blew up in 2013 over the arrest of an Indian diplomat, Devyani Khobragade, for visa fraud and underpaying a domestic worker who was later given a U.S. "T visa" issued to trafficking victims.

Khobragade`s arrest and strip search provoked an outcry in India and the issue has festered, although U.S.-India relations have strengthened since Modi came to power in May 2014, with both sides stressing shared strategic interests.

U.S. officials say Indian citizens who have been issued U.S. T visas have been subject to restrictions, including long delays in renewing passports at Indian consulates in the United States.

Between July 2014 and March 2015, the crackdown was harsher, with authorities at Indian airports confiscating at least 20 passports stamped with U.S. T visas confiscated. This prevented trafficking victims who went home to collect their families from returning to the United States.

Berry is Washington`s first gay-rights ambassador and a U.S. official said no trafficking czar had visited India for the past eight years.

The India ambassador played down the impact of the trafficking issue on U.S.-India relations, saying these were "at a very good stage now." with two visits by Modi to the United States, and Obama becoming the first U.S. president to visit India twice while in office.

"These are all reflections of where the relationship is headed," he said.

India was happy to work in an international framework to tackle the problem of trafficking, but rejected "unilateral assessments" of another country," he said.

"We will never accept it," he said.

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