President Marcos said that the call to separate Mindanao from the rest of the Philippines is "doomed to fail" as it is a grave violation of the 1987 Constitution.

Marcos said this after his predecessor, former president Rodrigo Duterte, suggested Mindanao's secession amid efforts to change the Constitution via people's initiative.

In a speech during the celebration of Constitution Day in Makati, the President said that separating Mindanao from the rest of the country will not happen.

"The new call for a separate Mindanao is doomed to fail for it is anchored on a false premise, not to mention a sheer constitutional travesty," he said.

"It is a grave violation of our Constitution. Hindi ito ang Bagong Pilipinas na ating hinuhubog, bagkus ito ay pagwasak sa ating bansang Pilipinas (This is not the New Philippines that we are forming but it is destroying our country)," he added.

According to Marcos, the 1987 Constitution does not allow the breaking up of the country.

"The Constitution calls for a united undivided country. It calls for eternal cohesion," he said.

"Unlike in other constitutions, there is nothing in ours that allows the breaking up of this union, such as an exit provision," he added.

The President then vowed that his administration would do everything to quell such efforts.

"The Constitution does not recognize the right to rebellion, while our criminal laws punish it," he said.

"The government has sternly enforced these laws to the letter and spirit, and this administration will be no exception," he added.

Marcos reiterated that he will not let the national territory be diminished, not even by a square inch.

"We will continue to defend from any threats, external and internal. We will not allow even an iota of suggestion of its breaking apart," he said.

"On this part of the Constitution, there is simply no dynamism or flexibility. This is my guarantee not only throughout this term but up to my dying breath," he added.

President Marcos said that even the people of Mindanao are against the idea of being separated from the entire Philippines.

"The current leadership of BARMM (Bangsamoro Autonomous Region in Muslim Mindanao) itself has repudiated this preposterous proposal and so did the other political leaders of Mindanao," he said.

"There is already genuine and effective local autonomy throughout our country, especially in the BARMM, without compromising our national integrity in the slightest degree," he added.

The Chief Executive asked the public to remain united against efforts to sow division among the people.

"Under the banner of the rule of law, the supremacy of the Constitution, our unity, both of our people and our territorial domain, will continue to fuel our ascent and the further pursuit of our collective goals and aspirations as a nation," Marcos said.

"We must galvanize our people and rally them to preserve our republic and everything that our flag symbolizes, its three stars and its sun. Huwag natin talikuran ang ating bandila (Let us not turn our backs on our flag)," he added.