MANILA, Philippines — A member of a consultative committee that President Rodrigo Duterte appointed to review the 1987 Constitution said he would propose the inclusion of Sabah in the Philippine territory as part of the country’s shift to a federal system of government.

"There should be a way that is acceptable under international laws to assert our claim to Sabah," former Senate president Aquilino Pimentel Jr. said in an interview with ANC.

"I think we can defer it a little bit more but to say that we stop doing it is not in the context of my proposal,” he added.

The switch to a federal system was one of the key planks of Duterte’s election campaign. The country currently employs a unitary form of government with much of the power emerging from the central government.

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Under Pimentel’s proposal for a new federal government, as reported by ANC, the Philippines will be divided into 12 federal states: Northern Luzon, Central Luzon, Southern Luzon, Bicol, Eastern Visayas, Central Visayas, Western Visayas, Minparom, Northern Mindanao, Southern Mindanao, and Bangsamoro.

Metro Manila will be the "federal capital," Pimentel said, adding that Sabah could be the 13th federal state.

"Eventually once we have asserted our sovereignty and rights over Sabah, we should include Sabah. Not only Sabah, but also Scarborough, Benham Rise, and Spratlys," Pimentel said.

The Sulu sultanate used to rule over parts of southern Philippines and Sabah. In 1963, the British government transferred Sabah to the Federation of Malaysia.

The Philippines claims that Sabah was only leased, not ceded, to the British North Borneo Co. The heirs of the sultan of Sulu continue to receive lease payments for Sabah.

Malaysia, however, maintains that the international community has been recognizing Sabah as part of its territory since the formation of the federation in 1963.

The dispute over Sabah landed on the headlines again in 2013 after shootouts sparked between armed members of a Filipino faction staking an ancient claim on Sabah state and Malaysian authorities.

READ: Duterte to pursue Sabah claim