"We protest the detention of Bishop George Ninan at Singapore airport on Tuesday," the Campaign and Advocacy for Human Rights (CACH) said in a statement.

CACH said Ninan was returning to Bombay after attending the annual Christian Conference of Asia in Indonesia, when immigration authorities held him incommunicado for 10 hours in a detention centre at Singapore airport.

"Bishop Ninan had more than 10 hours of transit time at Singapore before he could catch a connecting flight ... He approached the immigration officer for a temporary pass to go out of the airport premises for a meal.

"The immigration officer accepted his request and was about to issue a pass to him when the computer showed up his name as one of those not permitted to enter Singapore."

The group said Singapore authorities confiscated his passport and only returned it to him on his arrival at India's Bombay airport.

The bishop is the secretary of the Joint Council of (Protestant) Churches in India.

Ninan was one of the Singapore-based staff members of the Christian Conference of Asia when it was expelled from the country 13 years ago, CACH said.

"We protest this violation of human rights and are co-ordinating with global church groups to send protest letters to the Singapore government," a CACH spokeswoman said.