"He has to show proof (that the cancellation of the HSR project) is a mistake", he said.
Mahathir said during the press conference that Malaysia may have to pay Singapore around Ringgits 500m ($US 126m) to extricate itself from the 2016 accord.
Prior to Mahathir's comeback, he served as prime minister from 1981 to 2003, a period which saw a rocky relationship between Malaysia and Singapore.
THE investigation into Prime Minister Dr Mahathir Mohamad under the Anti-Fake News Act following his statement that his jet was sabotaged during GE14 will likely be dropped. Helmed by Khaw Boon Wan, the Ministry had set aside S$3 billion in its budget for FY2018 for the Kuala Lumpur-Singapore High-Speed Rail (HSR) and the Johor Bahru-Singapore Rapid Transit System (RTS) Link.
Jurong Lake District is where the terminus for the high speed rail was to have been sited - into Singapore's second central business district.
Additionally, the Urban Redevelopment Authority had previous year unveiled plans to turn the Jurong Lake District into Singapore's second Central Business District.
"We have to talk with Singapore about dropping that project", he said.
The 92-year-old veteran politician said: "We need to do away with some of the unnecessary projects, for example the high-speed rail, which is going to cost us RM110 billion (US$28 billion) and will not earn us a single cent. That will be dropped", Mahathir told the Financial Times.
When asked if there are any plans to renegotiate another mega project, the East Coast Rail Link (ECRL), Dr Wan Azizah said the terms relayed to the federal government were "very strange".
Newly minted Prime Minister Dr Mahathir Mohamad believes that the move by Malaysians to vote BN out of power on May 9 for the first time in the country's history may inspire neighbouring Singaporeans, who have also been under one-party rule since independence. He added: "Mostly it was about trying to make the prime minister popular and it cost billions of dollars".