Philippine President Rodrigo Duterte said on Wednesday he ordered the investigation into a 71-year-old Australian nun for "disorderly conduct," justifying it as a legal move against "undesirable" foreigners.

Sister Patricia Fox, a coordinator of a Philippine congregation of Catholic nuns called Notre Dame de Sion, was taken from her house this week and detained at the immigration bureau in Manila for almost 24 hours.

She was released on Tuesday pending further investigation.