De facto Malaysian opposition leader Anwar Ibrahim has urged his Parti Keadilan Rakyat (PKR) to resist joining hands with influential Umno figures in a campaign to unseat embattled Prime Minister Najib Razak.
The former deputy prime minister had earlier supported the so-called Citizens' Declaration calling for Mr Najib to resign amid accusations of corruption.
But in a handwritten letter from jail - where he is serving time for a controversial sodomy conviction - he warned the opposition not to dive headlong into former premier Mahathir Mohamad's campaign, which is "flawed and inconsistent with reforms" pursued by Anwar's party.
"Unfortunately, this will only convince Mahathir to continue to feel no guilt over the destruction and waste that happened in his time," he said in the letter, which PKR leaders, speaking to The Straits Times, said was read out to a meeting of the leadership last week.
He also accused Tun Mahathir and his ally Daim Zainuddin - former finance minister and widely seen as a mover and shaker in Umno - of teaming up to maintain the sway of the political establishment and their cronies that "caused destruction which we feel to this day".
Anwar was Dr Mahathir's deputy until 1998, when he was sacked from government and later jailed for abuse of power and sodomy.
The sodomy charge was overturned in 2004, allowing Anwar to lead the opposition to unprecedented gains in recent years.
But he was imprisoned again in February last year on a new sodomy charge, and without him at the helm, the opposition alliance broke up and Parti Islam seMalaysia (PAS) decided to go its own way.
As Mr Najib came under increasing pressure following revelations last July that almost US$700 million (S$961 million), allegedly linked to state investor 1Malaysia Development Berhad (1MDB), was deposited into his personal bank accounts, it was Dr Mahathir - still influential despite retiring in 2003 - who led the charge.
Attorney-General Mohamed Apandi Ali in January said no criminal offence was committed by Mr Najib, who said the money had been a donation from the Saudi royals, and most of it had been returned.
Mr Mahathir has toured the country, calling for Malaysians and Umno leaders to turn against Mr Najib, and declared last week that a Save Malaysia movement had amassed 1.2 million signatures endorsing the Citizens' Declaration.
In his letter, Anwar said it would be naive to think "Mahathir is now more open to change" and lamented the pressure faced by his wife and daughter to meet Dr Mahathir.
Both have stayed clear of events spearheaded by Save Malaysia.
Anwar, 68, also referred to another attempt to dislodge Mr Najib, allegedly led by Umno's longest-serving lawmaker, Tengku Razaleigh Hamzah.
"We were so excited at the thought of or we were so desperate to change the national leadership that we committed (to the statutory declaration plot). Today, it is fodder for ridicule, especially after Ku Li himself denied his involvement," Anwar wrote. Tengku Razaleigh's nickname is Ku Li.
He also said "rivalry (within PKR) has gone beyond the boundaries of ethics that it seems to be better to deal with political enemies rather than comrades".
Anwar's wife and PKR president Wan Azizah Wan Ismail yesterday said the letter was an "internal matter" asking the party to "be cautious. That's it".