MANILA (UPDATED) — Retired Supreme Court Senior Associate Justice Antonio Carpio on Thursday accepted President Rodrigo Duterte’s challenge to a debate on the West Philippine Sea issue and urged the chief executive to resign immediately for making a false claim about him.

Duterte recently sought to blame the administration of his predecessor, former president Benigno Aquino III, for the loss of Scarborough Shoal in 2012 following a standoff with China. On Wednesday night, he dared Carpio to debate on the issue.

"I gladly accept the challenge anytime at the President’s convenience," Carpio said in a statement to the media.

The President also alleged that Carpio and former Foreign Affairs Secretary Albert Del Rosario were involved in the withdrawal of Philippine ships from Scarborough Shoal eight years ago. Duterte offered to resign if proven he is lying.

Both Carpio and Del Rosario were part of the Philippine team that pursued an arbitration case against China over incursions into the country's exclusive economic zone in the South China Sea in 2013, which led to a ruling that invalidated China's 9-dash line claim in 2016, shortly after Duterte became President.

On Wednesday night, Duterte, who has been cozying up to China, called this ruling just a piece of paper.

"President Duterte should now resign immediately to keep his word of honor," Carpio said, issuing a swift rebuttal.

"I state under oath that I was never involved in the decision to withdraw Philippine Navy ships from the West Philippine Sea during the 2012 Scarborough standoff. I was serving in the Supreme Court at that time and all I knew about the withdrawal of Philippine Navy ships was what I read in the newspapers," he said.

The shoal is within the Philippines' exclusive economic zone in the South China Sea and has long been traditional fishing grounds for Philippine fishermen.

2012 STANDOFF

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Philippine and Chinese ships figured in a standoff at the shoal after Filipino naval officers attempted to arrest Chinese fishermen seen illegally fishing in the area but were blocked by China's surveillance vessels.

Del Rosario said the US brokered a deal to end the standoff, and that China and the Philippines agreed to withdraw their ships from the area at a certain hour.

But Beijing "deceitfully breached our agreement by not withdrawing their 30 or more ships," he said.

• Duterte told about China's control of Scarborough Shoal; Beijing breached pull-out deal

Almost a decade later, Chinese vessels continue to encroach into the Philippines' EEZ in the waters.

• About 200 ships still moored at West Philippine Sea, geo-analyst says
• Philippines rejects Chinese fishing ban in West Philippine Sea

Del Rosario and Carpio said Duterte "unfortunately" set aside the arbitration ruling in exchange for up to $24 billion in Chinese investment and aid pledges.

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

WHAT DUTERTE SAID

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Duterte on Wednesday called the arbitral ruling a piece of "paper," which he said led to nothing.

"Tapos sabi nila itong papel sa kaso nanalo tayo, i-pursue mo. Pinursue ko, walang nangyari," Duterte said. "Actually sa usapang bugoy, sabihin ko sa ‘yo, bigay mo sa akin, sabihin ko, ‘P***** *** papel lang ‘yan, itatapon ko ‘yan sa wastebasket.'"

(They tell me to pursue this paper because we won. I pursued it but nothing happened. Actually, if you give that to me, I will tell you, 'Son of *****, I will throw that in the wastebasket.')

He also threatened to "execute" Del Rosario "by hanging" if the former official fails to explain why Philippine ships withdrew from Scarborough.

Duterte also challenged Carpio to a debate, saying he would only ask Carpio about who ordered the retreat, what the Aquino administration did after, and whether or not the Philippines could enforce the 2016 arbitral award.

"Itong Carpio naman, sulat nang sulat ng mga decision para sa kanyang utak lang. Isa ring ugok itong… Pareho man tayo abogado. Gusto–eh gusto mo magdebate tayo?" said the President, a former prosecutor.

(This Carpio writes and writes decisions just for his brain. This one is rotten, too. We are both lawyers. Do want us to debate?)

He said he "never asked anything" from China.

"I was asking [for] friendship, that was all," said Duterte.

"Kung ako'y nagsisinungaling, mag-resign ako bukas kaagad," he added.

(If I am lying, I will resign immediately tomorrow.)

Facing growing domestic pressure to take a harder line, Duterte said last week the Philippine maritime patrols would continue, insisting its sovereignty over the waters was not negotiable.

• Carpio, Del Rosario hit back at Duterte tirades over West Philippine Sea
• Palace: Duterte 'clear' he had no vow to take back West Philippine Sea
• Duterte: Philippines grateful to China, but West Philippine Sea 'cannot be bargained'

The Philippine Bar Association, the oldest organization of lawyers in the country, on Thursday offered to host the debate for free and "provide a balanced arena."

"The Filipino public will benefit immensely from a frank and straightforward discussion on a matter that affects the entire citizenry," the group said in a statement.

Carpio said he was "happy" to accept the group's offer.

– With report from Jamaine Punzalan, ABS-CBN News; Agence France-Presse