"The idea that Rohingya refugees have been cast into the sea from naval vessels is nothing short of outrageous," said Tom Andrews, the United Nations special rapporteur on the rights situation in Myanmar.

"I am seeking further information and testimony regarding these developments and implore the Indian government to provide a full accounting of what happened."

Andrews, who is an independent expert mandated by the UN Human Rights Council but who does not speak on behalf of the UN itself, said he was "deeply concerned by what appears to be a blatant disregard for the lives and safety of those who require international protection".

The mostly Muslim Rohingya have been heavily persecuted in Myanmar for decades.

One million Rohingya live in a string of squalid camps in Bangladesh after escaping a 2017 military crackdown in Myanmar.

Thousands of them risk their lives each year on long sea journeys to seek refuge elsewhere.

Andrews' statement pointed to reports that Indian authorities last week detained dozens of Rohingya refugees living in Delhi, "many or all of whom held refugee identification documents".

Around 40 members of the group were reportedly blindfolded and flown to the Andaman and Nicobar Islands and then transferred to an Indian naval ship, he said.

"After the boat crossed the Andaman Sea, the refugees were reportedly given life jackets, forced into the sea and made to swim to an island in Myanmar territory," he said.

"Such cruel actions would be an affront to human decency and represent a serious violation of the principle of non-refoulment," he said, pointing out that Rohingya "face the threat of violence, persecution and other grave human rights violations in Myanmar".

"The government of India must immediately and unequivocally repudiate unconscionable acts against Rohingya refugees, stop all deportations to Myanmar and ensure that those responsible for these blatant violations of India's international obligations are held responsible," Andrews said.