MANILA - Philippine Senator Imee Marcos, chair of the Senate Committee on Foreign Relations, on Thursday said there were "glaring violations" of former President Rodrigo Duterte's rights in the arrest on March 11.

ALSO READ: Senator Marcos seeks clarity on ex-president Duterte's ICC arrest

Marcos released the preliminary findings by the Senate panel at a press conference, saying that the Philippines had no legal obligation to arrest Duterte and turn him over to the International Criminal Court (ICC) in The Hague in the Netherlands.

Marcos, an elder sister of Philippine President Ferdinand Romualdez Marcos, said the initial probe also showed that the Philippine government decided to assist the ICC to arrest Duterte, and that the administration "already started preparations prior to March 11."

READ MORE: Philippine senator calls for urgent probe into ex-President Duterte's arrest

On March 11, Duterte was detained upon his return to Manila from abroad, following an arrest warrant issued by the ICC over his "war on drugs" campaign, a move he has questioned. He was surrendered to the custody of the ICC on March 12 after being flown from Manila to the Netherlands.