SINGAPORE — In an unusually public escalation of a feud within Singapore’s first family, Prime Minister Lee Hsien Loong’s siblings have accused him of misusing his position to advance his personal agenda and of betraying the legacy of their father, Singapore’s first prime minister, Lee Kuan Yew.

“We feel big brother omnipresent,” the prime minister’s sister, Lee Wei Ling, and brother, Lee Hsien Yang, wrote in a statement posted on Facebook on Wednesday. Lee Hsien Yang added that he planned to leave Singapore “for the foreseeable future” because of his brother.

The prime minister, who is on an overseas trip with his family, issued his own statement, rejecting the allegations.

“I am very disappointed that my siblings have chosen to issue a statement publicizing private family matters,” he wrote on his Facebook page. “Since my father’s passing in March 2015, as the eldest son I have tried my best to resolve the issues among us within the family, out of respect for our parents.”