MANILA — President Rodrigo Duterte "has nothing to prove," Malacañang said on Monday, after the Chief Executive challenged a retired Supreme Court justice to a debate on the West Philippine Sea and then backed out when the magistrate accepted the challenge.

Duterte last week dared retired Supreme Court justice Antonio Carpio to face-off about Manila and Beijing's maritime row, which the latter accepted. The President, however, backed out of the debate and tapped his spokesman Harry Roque as his proxy, which drew accusations of cowardice.

Addressing the hashtag #DuterteDuwag (coward) that trended after, Roque pointed out the Chief Executive debated at least 5 times with his rivals for the presidency in 2016.

"He has nothing to prove," Roque said in a press briefing.

"Tapos na siya d'yan (he is done with that)," he added.

He urged the public to study the legal reasons behind Duterte's withdrawal from the debate.

"As President everything that he can say... becomes presidential proclamations and binding," Roque said. "Mahirap naman po 'yon (that is difficult)."

"Mayroon talagang mga bagay-bagay na should remain confidential, pursuant to executive privilege dahil ang mga desisyon ng Presidente dapat tamang desisyon, maski hindi po iyan popular na desisyon," he said.

(There are really some things that should remain confidential, should remain confidential, pursuant to executive privilege, because the President should make the right decision, even if it's not popular.)

Duterte has blamed the administration of his predecessor Benigno Aquino III over the loss of Scarborough Shoal in the West Philippine Sea after a standoff in 2012.

Albert del Rosario, who served as Aquino's foreign affairs chief, said China "deceitfully breached" its agreement with the Philippines to end their standoff by withdrawing ships from the area.

Del Rosario in 2014 pursued an arbitral ruling against China, a move that Carpio backed.

Shortly after Duterte took office in 2016, a United Nations-backed court ruled in favor of the Philippines and junked Beijing's claims to about 90 percent of the South China Sea, within which is the smaller West Philippine Sea.

Duterte has refused to press China to obey the ruling and sought investments and loans from the economic superpower.

The President last Wednesday called the arbitral ruling a piece of "paper," which he said led to nothing.

• China, not Duterte, will throw away Philippines' arbitral victory, says Palace

Beijing and Manila's maritime dispute flared up again in March after hundreds of Chinese boats were spotted inside the Philippines' Exclusive Economic Zone.

• Rouse him from 'sleep under his kulambo': Carpio cites Duterte's 'self-inflicted' blows favoring China on sea dispute

China has refused repeated calls from the Philippines to withdraw the boats, and tensions have intensified as Manila stepped up maritime patrols in the area.

– With a report Agence France-Presse

Video courtesy of PTV