Lee Hsien Loong said that he is "deeply saddened" that his sister Lee Wei Ling had accused him of abusing his power to commemorate the first anniversary of their father's death in order to establish a dynasty.

"The accusations are untrue," the prime minister said of the comments by Dr Lee, a well known neurosurgeon, on her Facebook page.

The feud is a political bombshell in Singapore where the People's Action Party founded by the elder Mr Lee has remained solidly united since taking power in 1959.

Prime Minister Lee has in the past sued critics for suggesting nepotism in his government.

The feud is being reported openly in Singapore's state-controlled media.

The Straits Times reported on Monday that Dr Lee had written a series of posts on Facebook over the past fortnight expressing her disagreement over the activities held to mark the anniversary on March 23.

Mr Lee Kuan Yew, who died aged 91, was a towering figure on the international stage who turned Singapore from being a backwater island at the tip of the Malaysian peninsula into a glittering regional financial and technology powerhouse with a US$300 billion a year economy.

Channel News Asia, a government-supported television station and website, reported that Dr Lee posted on Facebook on Sunday that the government was trying to use the occasion of her father's anniversary to "hero worship" him.

Dr Lee had reproduced correspondence she had had with editors of the Straits Times over the draft of an opinion piece on the anniversary programs she had written.

The piece was not published by the Straits Times and was eventually posted in full on Dr Lee's Facebook page.

Channel News Asia said that in one of the emails released by Dr Lee, she said she and her brother "are at odds on a matter of principle" with regard to the commemoration and that her brother had "no qualms (about) abusing his power to (have) a commemoration just one year after Lee Kuan Yew died."

She added: "Let's be real, last year's event was so vivid, no-one will forget it in one (year). But if the power that be wants to establish a dynasty, LKY's daughter will not allow LKY's name to be sullied by a dishonourable son."

The post was taken down later on Sunday, but the prime minister fired back on his own Facebook page a few hours later, saying the idea that he wanted to establish a dynasty does not make sense.

"Meritocracy is a fundamental value of our society, and neither I, the PAP, nor the Singapore public would tolerate any such attempt," he said.

Prime Minister Lee said the first anniversary of a person's passing was a significant moment "to remember him and reflect on what he meant to us."

"The more so with Lee Kuan Yew," he said.

The prime minister said his cabinet had discussed how the occasion should be marked and his advice was that it should be left to ground-up efforts, with observances kept in proportion, and focused on the future.

"The cabinet recognised the strong desire of many Singaporeans to show their respect for Mr Lee, and honour what he did for us," he said."

"We reviewed the events and observances that different groups had planned and agreed that they were generally appropriate … they expressed the sincerity felt sentiments of Singaporeans, which my cabinet colleagues and I deeply appreciate."

Mr Lew Kuan Yew ruled Singapore from 1959 until 1990.

His death sparked a massive outpouring of grief among Singaporeans and more than 100 events were held to mark the one year anniversary.

Prime minister Lee, 64, has ruled the country since 2004.

With agencies