SINGAPORE: A new opposition party backed by the estranged brother of Singapore's prime minister was launched Saturday in a fresh challenge to the government as speculation mounts elections could be called soon.

The Progress Singapore Party (PSP) -- aiming to contest an election due by 2021 but widely expected earlier -- is led by Tan Cheng Bock, a medical doctor and former government stalwart who once ran for president and nearly defeated the establishment candidate.

The group has received the support of Prime Minister Lee Hsien Loong's brother, the latest sign of a bitter falling-out within the city-state's first family over their father's legacy.

The rare row within Singapore's elite erupted following the 2015 death of the men's father, founding leader Lee Kuan Yew, who led the country for three decades and is widely revered in the city.

Under decades of rule by his People's Action Party (PAP), Singapore transformed from a gritty port into one of Asia's most advanced economies -- although authorities also faced criticism for curtailing civil liberties and free speech.

Party officials said that Tan's PSP was formally launched in the morning at an event attended by hundreds of supporters. He was due to address hundreds more supporters and the media in the afternoon.

The group joins a handful of other parties seeking to take on the dominant PAP, but the fractious opposition -- which has just six out of 89 elected seats in parliament -- is not viewed as a serious threat.

However, backing from the premier's sibling, Lee Hsien Yang, could provide a boost to 79-tear-old Tan, who has slammed what he described as eroding standards of governance in Singapore.

In January, 62-year-old business executive Lee said in a Facebook post that Tan was "the leader Singapore deserves".

"I wholeheartedly support the principles and values of the Progress Singapore Party. Today's PAP is no longer the PAP of my father. It has lost its way," he said in another post last week.

During a press conference last week, Tan said he may be willing to take Lee into the party formally.

Lee Hsien Yang's association with the party can boost Tan's profile as "one of the 'nice' people to have represented the PAP during its glory days," said Michael Barr, a Singapore politics specialist at Flinders University in Australia.

"The presence of the prime minister's brother in, or at least on the fringes of an opposition party, is a reminder that Prime Minister Lee Hsien Loong is not his father... and that this family is fractured over Lee Kuan Yew's legacy," Barr told AFP.

Lee Hsien Yang's candidacy under the PSP would be a "game-changer" as it would "do immense damage to the brand of Lee Hsien Loong's branch of the family".

However, law lecturer Eugene Tan from the Singapore Management University said Lee Hsien Yang's support for the party is a "double-edged sword" as it could overshadow the PSP's agenda and focus attention to the family feud.

"The vision that Dr Tan may have will become a sideshow. So it is a card that needs to be played very, very carefully," political analyst Tan told AFP.

The Lee family row centres on allegations made by the premier's siblings that he is seeking to block the demolition of a family bungalow to capitalise on their father's legacy -- something he has denied. —AFP