Singapore Prime Minister Lee Hsien Loong's younger brother Lee Hsien Yang said on Wednesday he felt "compelled" to leave the city state amid a family dispute, which started with their father's death two years ago.

"It is with a very heavy heart that I will leave Singapore for the foreseeable future," Lee Hsien Yang wrote in a six-page joint statement with his sister Lee Wei Ling that was posted on his Facebook account. "I have no desire to leave. Hsien Loong is the only reason for my departure," they said.

"We do not trust Hsien Loong and have lost confidence in him," the siblings said in their statement. It did not mention where Lee Hsien Yang planned to relocate.

The prime minister issued a statement denying allegations made by his siblings and said he regretted their public comments, which escalate a feud that has simmered since the March 2015 death of their father Lee Kuan Yew, Singapore's first elected prime minister.

The tensions have largely stayed removed from domestic politics and the ruling People's Action Party led by Lee Hsien Loong has a strong grip on power. It boosted its share of the popular vote in the last election in September 2015 to nearly 70 per cent - the highest since 2001 - and secured 83 of 89 seats up for grabs.

"I am very disappointed that my siblings have chosen to issue a statement publicising private family matters," Prime Minister Lee said in an emailed response on Wednesday. "While siblings may have differences, I believe that any such differences should stay in the family."

Lee Hsien Yang and Lee Wei Ling's statement has hurt their father's legacy, the prime minister said. He denied an "absurd claim" alleging he harboured political ambitions for his son. Lee, who became Singapore's third prime minister in 2004, said he would consider the issue further after he returned from an overseas trip with his family later this month.

Lee Hsien Yang is chairman of the Civil Aviation Authority of Singapore and special adviser to private-equity firm General Atlantic. He and Lee Wei Ling said in the statement they were "disturbed by the character" and "personal agenda" of Lee Hsien Loong. They said their statement was "by no means a criticism of the government".

Six months after the elder Lee died, his two younger children filed a legal challenge against the government relating to an agreement over the custody and use of certain interviews by their father.

The late Lee's house, located on the fringe of the Orchard Road shopping belt, has also been the subject of dispute. The late premier had said he wanted his home demolished after his death. There have been calls to convert the home into a museum and as a memorial to him. In December 2015, Lee Hsien Loong said he recused himself from all government decisions involving the house.

Lee Kuan Yew, who was prime minister from 1959 to 1990, turned Singapore into Southeast Asia's richest nation by opening the island to foreign investors. He ran a tightly-controlled state that emphasised incorruptibility and stability. Lee stepped down from the cabinet in 2011.