Prime Minister Lee Hsien Loong had "threatened angrily" to gazette 38, Oxley Road as a national monument after the death of their father Lee Kuan Yew, his sister Lee Wei Ling claimed.

In a Facebook post yesterday, Dr Lee said this happened after Mr Lee's will was read to the family, and PM Lee's actions "greatly disturbed" her.

"He was willing to go against Papa's wishes as soon as Papa was gone. He is a dishonourable son," she wrote.

Gazetting the house as a national monument would ensure its preservation, and prevent its demolition.

Dr Lee's latest salvo in the ongoing dispute between the Lee siblings comes before a Parliament debate starting tomorrow on the issue and its implications on the integrity of the Government.

PM Lee will make a ministerial statement addressing the allegations of abuse of power that his siblings, Dr Lee and Mr Lee Hsien Yang, have made.

The Lee siblings are tangled in a dispute over their father's Oxley Road house. Both Dr Lee and Mr Lee Hsien Yang want to demolish the house, an act that would be in accordance with their father's wishes, they say.

They have also claimed that PM Lee wants to preserve the house for political gain, although PM Lee has made clear that as a son, he supported his father's wish for demolition.

Dr Lee also took issue with what she called PM Lee and his wife Ho Ching's attempt to build a "Lee family cult".

She said that when Ms Ho took a sabbatical in 2015 from her position as chief executive of Temasek Holdings, she had spent her days at the Oxley Road house "getting the photographer from Ministry of Communications and Information (MCI) to photograph and catalogue items, which she would pack into plastic boxes to send to storage and (recreating) the way Oxley looked decades ago".

"She had no business doing this at all," said Dr Lee.

Yesterday, an MCI spokesman said in reply to media queries that MCI photographers continued to support Mr Lee after he stepped down from Cabinet, "in line with MCI's policy of supporting former prime ministers and presidents after they leave office".

"After Mr Lee's passing, MCI photographers were deployed to take photos of various personal and official items belonging to Mr Lee at 38, Oxley Road.

"This was done for the purposes of national archival and documentation. Similar photographic recordings were done during Mr Lee's lifetime of his study at home and of the basement dining room," said the spokesman.

Dr Lee also said that Ms Ho had wrongfully taken and handed items from the house to the National Heritage Board (NHB) for a memorial exhibition, which the NHB at first accepted without protest.

Yet later, NHB was subsequently told by the Prime Minister's Office to refuse the exhibition as she and Mr Lee Hsien Yang had required the part of their father's will expressing his desire for the house to be demolished to also be displayed, Dr Lee said.

"Hsien Loong and Ho Ching angered me very early on. Both were not straight and were taking advantage of the fact that no one would dare criticise them for acting improperly," said Dr Lee.

Danson Cheong