Kuala Lumpur, Malaysia: Former Malaysian premier Mahathir Mohamad announced on Monday he was quitting the ruling party, saying it had degenerated into an organisation whose sole purpose was to protect scandal-plagued Prime Minister Najib Razak.

Mahathir has for months been a leading voice calling for the ousting of Najib, who is under pressure over allegations that billions of dollars had been pilfered from state firms, and for accepting a mysterious $681 million sum from an overseas source.

‘I want to leave UMNO because it is no longer UMNO,’ Mahathir was quoted saying, referring to the long-ruling United Malays National Organisation which he led as premier from 1981-2003. 

‘It is a party dedicated to protecting Najib,’ the news portal Malaysiakini quoted him saying.

Authorities in several countries are currently investigating money flows centring on a company launched by Najib called 1Malaysia Development Berhad (1MDB).

Swiss authorities have said they believe $4 billion may have been stolen from Malaysian state firms and have frozen millions in accounts linked to 1MDB.

After the scandals broke Najib sacked Malaysia's attorney general, who was reported to be preparing charges against the prime minister.

Najib installed his own appointee, who has brought domestic investigations to a halt.

He also purged his cabinet of critics and his government has arrested whistle-blowers and shut down media outlets that reported on the allegations.

Last week authorities began blocking access to The Malaysian Insider, a leading news portal, after it ran a story on the affair. 

Najib's attorney general also recently provoked howls of protest by abruptly clearing the premier of wrongdoing in the $681 million donation.

Through it all, the irascible and still-influential Mahathir has continued to savage Najib, accusing him of corruption, criminal activity and bribing party members to maintain their support and protect him from charges.

But Mahathir's campaign has largely failed to gain traction in a ruling party that analysts say is built on patronage and money politics.

- Charges of hypocrisy –

Najib is widely viewed as solidifying his hold on the powerful party and facing no apparent threat of ousting, and Mahathir's rejection of UMNO is seen as having little impact.

‘I don’t see a mass exodus of UMNO members despite the seriousness of the accusations against Najib because UMNO leaders depend on party largesse to survive. UMNO has consolidated behind Najib,’ said Ong Kian Ming, an opposition parliament member.

Mahathir also stands accused of hypocrisy.

He is accused of weakening institutions such as the judiciary during his own iron-fisted 22-year rule, and for setting a tone of repression by sacking and jailing his then-deputy Anwar Ibrahim in 1998 in a power struggle.

Anwar spent six years in jail on sodomy and corruption charges widely viewed as trumped-up. He later galvanised the opposition into a potent force after his release.

But last year Najib’s government jailed Anwar again for five years on new sodomy charges that have been widely criticised.

Earlier in February UMNO ousted Mahathir's son Mukhriz as chief minister of a northern state in what was widely seen as political payback for his father's criticism of Najib.

Mahathir has quit UMNO in protest before.

Five years after voluntarily stepping down in 2003, he quit amid a rift with his own hand-picked successor, then-premier Abdullah Ahmad Badawi, after the latter led UMNO to a poor electoral showing.

Abdullah eventually resigned under pressure.