MANILA (Reuters) - Bishops from an American Methodist church called for the Philippines on Tuesday to release a missionary from Zimbabwe, detained six weeks ago on suspicion of belonging to a “subversive” group.

Tawanda Chandiwana has been held at an immigration facility in Manila since May 9 following his arrest last month, while attending a seminar on the southern island of Mindanao, where government forces have been fighting Maoist-led insurgents for more than 50 years.

In February, he had been briefly detained and questioned, along with two other missionaries from the United Methodist Church, when they were stopped at a police checkpoint in Mindanao while participating in a human rights fact-finding mission sponsored by a left-wing group.

Immigration authorities have prevented his colleagues - an American and a woman from Malawi - from leaving the Philippines, according to a statement issued by the Global Ministries of the United Methodist Church.

“We vigorously protest this treatment of our mission personnel,” general secretary Thomas Kemper said in the statement. “It is unconscionable that Tawanda has been held for six weeks.”

Dana Sandoval, an immigration bureau spokeswoman, declined to comment, but promised to look into the missionaries’ cases.

President Rodrigo Duterte has openly attacked the Catholic Church and other religious groups that have been critical of his government’s brutal war on drugs and its human rights record.

Last week, the Philippine justice department struck down a deportation order issued by the immigration bureau against an Australian Catholic nun who had participated in a political rally.