MANILA – Former Foreign Affairs Secretary Albert Del Rosario on Tuesday criticized President Rodrigo Duterte for publicly expressing his willingness to sell Philippine-claimed islands in the South China Sea to Beijing, saying this could undermine the country’s standing on the dispute.

Before flying to Saudi Arabia on Monday, Duterte, known for his friendly stance towards China, had said he may consider selling Philippine islands in the South China Sea to Beijing if the country could get "very rich" from such a deal.

Malacañang meanwhile explained Tuesday that the President's statement was a "light-hearted" remark.

Del Rosario, one of the primary figures who led Manila’s South China Sea arbitration victory against China, said Duterte should avoid issuing such a statement as it does not serve the interest of the Philippines.

“As suggested earlier by [Supreme Court Associate] Justice [Antonio] Carpio, spur of the moment statements should be avoided. It puts us in a poor strategic position without the benefit of flexibility, especially if there is a need to negotiate,” Del Rosario said in a statement.

• Read: Carpio tells Duterte what to do re China in Scarborough Shoal

“The legality of statements made is not clear and should be studied. It could be a very thin line since it can be further argued that the Palace is not faithfully executing its role to defend what is ours.”

Since assuming the presidency, Duterte has sought to forge closer ties with China following years of animosity over the sea dispute during the administration of his predecessor Benigno Aquino III.

Duterte’s critics have said his “defeatist” stance in the South China Sea dispute has made the Philippines prone to abuse by its wealthy and powerful neighbor, which claims nearly the entire sea as part of its territory.

While Manila’s arbitration victory against China cannot be reversed, Del Rosario said such statements “could undermine our ability and that of other nations to implement the outcome.”

“It gives our northern neighbor the political momentum to persist in its unlawful expansion agenda,” he said.

In Saudi Arabia, where Duterte is currently on a state visit, Presidential Spokesperson Ernesto Abella said the president’s statement only aimed to underscore the growing friendship between the Philippines and China despite the bitter dispute.

“Basically, it was a lighthearted way of saying ‘we are friends,’” Abella told reporters in Riyadh.

“If you notice the context, it says: ‘When there’s no more trouble, when we are rich enough.’ In a sense, that’s really a thing that is in the far future that will be [the] end result of our friendship and negotiations with China.”

The Philippines scored a landmark victory against China in July last year, when the United Nations arbitral tribunal invalidated Beijing's nine-dash line claim over almost all of the South China Sea.

China has refused to recognize the ruling, asserting its "indisputable sovereignty" almost all of the disputed waters. It has instead ramped up militarization and reclamation activities in South China Sea territories.

Manila and Beijing are set to hold long-stalled bilateral talks on the dispute in May.

• Read: Philippines, China to hold direct talks on sea row: Manila