The Ministry of Home Affairs (MHA) has responded to three activists who had filed a complaint with the Prime Minister for what they charged were "highly irresponsible" remarks made by a government minister and an MP.
In its reply, MHA said the three had "crossed a red line by inviting foreign leaders to intervene in Singapore politics".
"The three individuals claim that they are patriots. It is not patriotic to invite any foreign leader to intervene in Singapore politics, especially the leader of a country who has declared his desire to increase the price of water to Singapore by more than 10 times, and with whom we seek to maintain close and friendly relations."
The MHA letter was signed by Mr Sunny Lee, who is press secretary to Home Affairs and Law Minister K. Shanmugam.
Mr Lee added that the minister stood by his comments.
Earlier yesterday, historian Thum Ping Tjin, journalist Kirsten Han and activist Jolovan Wham submitted a letter to Prime Minister Lee Hsien Loong, urging him to look into the conduct of MP Seah Kian Peng and Mr Shanmugam, whom they said had made public allegations "without adequate substantiation or evidence".
A separate letter, sent to MP Charles Chong, who chairs the Select Committee on Deliberate Online Falsehoods, said it was ironic that Mr Seah and Mr Shanmugam, both members of the Select Committee, "are themselves making public allegations without adequate substantiation or evidence".
The two People's Action Party (PAP) politicians had criticised the conduct of the trio, who were part of a group that met Malaysian Prime Minister Mahathir Mohamad last Thursday.
After the meeting, Dr Thum called on Tun Dr Mahathir to "take leadership in South-east Asia for the promotion of democracy, human rights, freedom of expression and freedom of information".
Referencing that post, Mr Shanmugam had said that "it is quite clear what that means". He added that it is an absolute no-no to invite a foreign politician to intervene in Singapore's domestic politics.
In their letter to PM Lee, the trio called on him as the PAP secretary-general to look into the issue and "take leadership in promoting responsible behaviour among members of your party".
PM Lee subsequently referred the activists' letter to Mr Shanmugam, the MHA said, adding: "The purpose of their letter is to divert attention from the conduct of the writers."
The ministry went on to recount the facts in this saga, noting that the trio met Dr Mahathir, along with political exile Tan Wah Piow and graphic novelist Sonny Liew, last Thursday.
The MHA said: "(Dr Thum) invited Dr Mahathir to address a conference about promoting democracy in South-east Asia, which obviously includes Singapore. Dr Thum also posted a photo of him presenting his book, about politics in Singapore, to Dr Mahathir.
"Mr Tan, a former Singaporean and a fugitive from the law, gave an interview after the meeting, also expressing the hope that Dr Mahathir and Malaysia could influence politics in Singapore.
"Mr Wham has asked 'what's wrong' in Dr Thum asking Dr Mahathir to bring democracy to Singapore, and that 'international political pressure is part of activism'.
"Dr Thum also believes that Singapore should be part of Malaya."
The MHA response also cited an Aug 9, 2016 post in which Dr Thum declared it was his "fervent wish" that Singapore "will one day return to our rightful place alongside our brothers and sisters in Malaya".
"This statement was made on Singapore's National Day. He has also made several other posts, to similar effect, about Singapore being part of Malaya."
The MHA statement concluded: "We can have vigorous debates within Singapore about our own affairs. But you cross a red line when you invite foreign powers or foreign leaders into Singapore politics."
Dr Thum and the others in the group have come under fire from netizens after Mr Seah wrote in a Facebook post last Saturday that the historian invited the Malaysian Prime Minister to bring democracy to Singapore, and that "it appears quite clear to me that PJ Thum does not wish Singapore well".
Mr Seah also criticised Dr Thum for suggesting that Singaporeans should rejoice on Malaysia's national day, which he termed as Singapore's "unofficial independence day".
Dr Thum was said to be referring to founding Prime Minister Lee Kuan Yew declaring on Aug 31, 1963 Singapore's independence from British rule, as part of a move to join Malaysia.
The activists, for their part, said in their letter to PM Lee that there was "no reference to bringing democracy to Singapore, nor any request to interfere in Singapore's affairs".
They added: "It is a huge stretch to suggest that wishing Singaporeans a 'happy unofficial independence day' is tantamount to expressing an opinion that Singapore is a part of Malaysia today."
They also said Mr Seah's comments had the effect of inciting accusations of treason. There have been calls for their arrest, detention and even death, they added.
In response, an MHA spokesman said yesterday that anyone who receives death threats should make a police report and the matter will be looked into.