JOHOR BARU - Johor's Crown Prince used the Malay word "Nyanyuk!" (senile) in an apparent response on Tuesday (Dec 11) to Prime Minister Mahathir Mohamad, who had a day earlier chided him over a controversy involving a protected mangrove-clad island in Johor.

The prince, Tunku Ismail Sultan Ibrahim, also issued a statement on his Facebook account on Monday to explain the controversy over Pulau Kukup, located in the Malacca Strait in southern Johor, which his father, the sultan, had wanted to convert from a national park to "sultanate land".

Tun Mahathir on Monday chided Tunku Ismail for saying that "an outsider" should not comment on issues involving Johor, including on Pulau Kukup.

Known as the world's second-largest uninhabited mangrove island, Pulau Kukup is one of five Ramsar sites in Malaysia. Ramsar sites are wetland sites accorded international importance under the United Nations' Convention on Wetlands.

Malaysians were surprised when it was recently revealed that the Johor state government, under Pakatan Harapan, had quietly degazetted the island to make it sultanate land of Johor controlled by the royal house.

Amid the brouhaha over the Johor move, Water, Land and Natural Resources Minister Xavier Jayakumar issued a statement last week saying the island should continue to be managed by the Johor state government.

In response, the Crown Prince wrote on his Facebook account last Saturday: "First of all, as an outsider, you don't need to meddle in matters related to Johor.

"Secondly, no matter what statement or letter is issued, you have no jurisdiction to override the Johor state Constitution. The only one who can change the Constitution is the ruler."

Dr Mahathir told the prince on Monday: "Malaysians are not outsiders. The federal government is not an outsider. We are responsible for all things in the country."

The premier also said that the island should not be developed.

On Monday, Tunku Ismail wrote on his Twitter account in a mix of Malay and English: "Who is developing Pulau Kukup?? Dah terangkan (I have explained) 4 times… Nyanyuk! (senile)"

The tweet has since been deleted.

Tunku Ismail also put up his explanation of the issue, saying Sultan Ibrahim wanted to change the island to sultanate land for better protection and preservation for future generations.

And the prince noted that Johor Menteri Besar Osman Sapian had, in fact, announced on Sunday that Pulau Kukup would remain a national park, after discussions with the Johor ruler.

"So do not make a non-issue into an issue, just to cover the weaknesses of the federal government's administration," Tunku Ismail wrote.