A public feud has erupted in Singapore’s first family, with the prime minister forced to issue a rebuttal after his sister accused him of abusing his political power over anniversary commemorations for the death of Lee Kuan Yew, the city state’s founding father.

The spat, which has played out on Facebook, follows a weekend post in which Lee Wei Ling accused Prime Minister Lee Hsien Loong of being a “dishonourable son” and of seeking to establish a political dynasty.

The rift is a rare display of acrimony among the city-state’s elite — censorship laws impose tight controls on the press, while defamation actions have been used to stifle critics, human rights groups say. The legacy of the country’s revered patriarch, who governed for more than three decades and was instrumental in Singapore’s economic transformation, is a particularly sensitive matter.