Former prime minister Dr Mahathir Mohamad has admitted that PKR de facto leader Anwar Ibrahim is one of Pakatan Harapan's prime minister candidates.

He was responding to a survey conducted by Invoke that found Anwar to be the most popular choice for prime minister among opposition supporters.

Mahathir however emphasised that Pakatan Harapan must first win the 14th general election.

"If we don't win, no one (from the opposition) can become prime minister. What's important is to win.

"Anyone can be a (prime minister) candidate," he told reporters after a ceramah by Parti Pribumi Bersatu Malaysia (Bersatu) last night.

Asked further whether the candidates would be named before the election, Mahathir said they could do so after Pakatan Harapan wins.

"If we don't win and name the candidate, it's like syiok sendiri (self-gratification)," he said.

Harapan has found itself in a dilemma about who its choice for prime minister should be.

At the PKR national congress on Sunday, leaders from PKR, DAP and Amanah raised placards naming Anwar as "the seventh prime minister".

Mahathir and Bersatu president Muhyiddin Yassin however did not partake in the stunt.

'Will probe 1MDB'

On another matter, Bersatu deputy chairperson Mukhriz Mahathir, who was also at the programme last night, mooted conducting investigations into financial scandals involving 1MDB should Pakatan Harapan come into power.

"Whoever is found guilty, we will throw them into prison. It doesn't matter whether he's the prime minister or not," he said.

This was supported by Muhyiddin who said that a commission will be formed to investigate the state investment fund.

"If Najib is found involved, he will be brought to face justice. If he is found guilty, he will be jailed. It's the same thing if (prime minister's wife) Rosmah (Mansor), (her son) Riza Aziz, or (businessman) Jho Low are involved.

"We will arrest everyone (found guilty). It's not because we are evil, but because this concerns the rakyat," he said.

Echoing this, Mahathir said they will find those responsible behind the scandal even down to the lubang cacing (wormholes).

"We will pull them by their short or long hair from the ground, and they will be prosecuted.

"What happened in Brazil will insyaAllah be done against such embarrassing criminals," he said.

Former Brazilian president Dilma Rousseau was impeached and removed from office for criminal administrative misconduct.

Replaced by current Brazilian President Michel Temer, the latter was accused of soliciting campaign donations for his party and both of them currently face trial over irregularities in their campaign funds.

Najib, meanwhile, continues to be accused of having received funds from 1MDB.

With regard to the much talked about RM2.6 billion donation, the prime minister has claimed it was from a Saudi royalty, and attorney-general Mohamed Apandi Ali, in clearing the prime minister of any wrongdoing in the matter, claimed US$620 million from the amount was later returned to the donor.

However, the US Department of Justice (DOJ) forfeiture suits related to 1MDB claims that an unnamed "Malaysian Official One" had received US$731 million said to have originated from the troubled firm.

Minister in the Prime Minister's Department Abdul Rahman Dahlan later confirmed that "Malaysian Official One " refers to Najib, but pointed out that since he was not named in the DOJ suits, the prime minister was not the subject of investigation.