The 35th ASEAN ( Association of Southeast Asian Nations) Summit officially opened on Sunday in Nonthaburi, Thailand with President Rodrigo Duterte joining the regional in the opening ceremony of the three-day summit.

Duterte is expected to discus among fellow heads of state about maintaining freedom of navigation and overflight on South China Sea.

He also pledged to resolve negotiations on the Code of Conduct over South China Sea dispute as ASEAN-China country coordinator

"The Chief Executive, in elaborating geopolitical transformation, mentioned the issue of the South China Sea, which he considers as one that is of strategic importance to ASEAN," Presidential Spokesperson Salvador Panelo said in a statement on Sunday.

"President Duterte articulated the firm stance of the Philippines on the issue, that is, the same must be resolved peacefully in accordance with international law, including the United Nations Convention on the Law of the Sea (UNCLOS)," Panelo added.

Duterte also urged ASEAN leaders to avoid choosing sides between China and United States on the changing regional landscape, said Panelo.

He said choosing sides between the two dominant countries can be considered as a "strategic mistake" done by previous Philippine leaders -- which the he claimed is now "rectifying through his independent foreign policy," Panelo pointed out.

"The Palace foresees the president to continue elaborating the position of our country in relation to important matters to ASEAN and discussing matters that are beneficial not just to the Filipino people but to the citizens of our neighbor countries in ASEAN for the remainder of this trip," said Panelo. Cristina Eloisa Baclig/DMS