A former spokesman of ex-president Rodrigo Duterte has dared China to release any document that would prove its claim that Manila had already agreed to remove the BRP Sierra Madre from a reef that Manila uses to press its stake in the Spratly Islands.

• Philippines denies promising China to remove ship from Ayungin
• China demands Philippines remove grounded ship from disputed waters

The BRP Sierra Madre -- deliberately grounded in 1999 in an effort to check the advance of China in the hotly contested waters -- has long been a flashpoint between Manila and Beijing.

A spokesperson for China's foreign ministry on Tuesday claimed the Philippines "has repeatedly made clear promises to tow away the warship illegally 'stranded' on the reef."

Atty. Salvador Panelo, however, challenged Beijing to show proof of such an agreement.

"Dapat ang China ipakita nila na may dokumento showing na nagcommit tayo, whatever kind of document. Ipakita niyo sa amin na meron kami commitment," he said during the Pandesal Forum at Kamuning Bakery.

He added that even if such an agreement exists, the Philippines is not bound by it since Manila already won an arbitral ruling that invalidates China's so-called 9-dash line in the whole of South China Sea.

"Ipagpalagay natin na meron nga, hindi ibig sabihin susundin namin ang commitment na 'yun...The circumstances have changed, hindi na po puwede because meron nang arbitral ruling..."

The Philippine military and coast guard have accused the China Coast Guard of breaking international law by blocking and firing water cannon against boats on a resupply mission to its garrison stationed on the BRP Sierra Madre at the weekend.

• Philippines slams China's use of water cannons at PCG boats in Ayungin Shoal

Beijing has defended its actions as "professional" and accused Manila of "illegal delivery of construction materials" to the grounded ship.

Panelo said the Philippines has filed a total of 440 diplomatic protests against Chinese intrusions in the West Philippine Sea.

He said President Ferdinand Marcos Jr. and Chinese President Xi Jinping should have a modus vivendi on the issue of the West Philippine Sea.

"Despite our protestations, despite our outrage, despite the expression of support and even the threat of the United States against China, it has remained unmoved," he said.