Sister Patricia Fox (second from the left) of the Notre Dame de Sion sisters, an Australian rural missionary and volunteer staff of Unyon ng mga Manggagawa sa Agrikultura (UMA), was taken into custody by immigration officers on Monday. Mark Saludes, ABS-CBN News

MANILA—(UPDATED) Immigration officials on Tuesday freed a 71-year-old Australian missionary whose detention sparked outrage among human rights groups who insisted who insisted her “activism is not a crime.”

Sister Patricia Fox was taken from her house and brought to the Bureau of Immigration office Monday after she took part in a human rights fact-finding mission in the troubled south.

Her detention came a day after Giacomo Filibeck, a Socialist Party official from the European Union who had criticized Duterte's brutal anti-drugs crackdown, was deported.

Fox was allowed to walk free "for further investigation," a Bureau of Immigration statement said.

The bureau added it had “established that the Australian nun holds a valid missionary visa and, thus, she is a properly documented alien.”

“While Fox was alleged to have taken part in protest actions by farmers in the past, she was not doing so at the time when (immigration) operatives served her the mission order yesterday,” the statement said, quoting lawyer Arvin Cesar Santos, who heads its legal division.

Fox will undergo a preliminary examination “to determine if deportation charges should be filed against her before the bureau’s board of commissioners,” the statement said.

She was not subjected to inquest because it applies “only to arrested after being caught in flagrante violating immigration laws.”

She was required to submit her passport, which showed her missionary visa is valid from Oct. 15, 2017 to Sept. 9 this year, the bureau said.

Fox is the superior of the Notre Dame de Sion in the Philippines, a congregation of Catholic nuns.

She had been involved with human rights missions in Mindanao, looking into the plight of indigenous people and farmers, left-wing lawmakers said, almost a year after President Rodrigo Duterte imposed martial law on the southern island of Mindanao.

Leftist lawmakers have vowed to hold a congressional inquiry into the deportation of foreign human rights advocates.