Dr Mahathir Mohamad has warned Umno elected representatives that future generations would censure them for allowing their party to be destroyed and a catastrophe to befall Malaysia.

In an open letter, Mahathir urged the elected representatives to join those who are calling for Prime Minister Najib Abdul Razak's resignation in order to rehabilitate Umno and redeem the pride of the race and nation.

Umno, he said, cannot be fixed from within as it is no longer the party it once was.

"What is left is Najib's party. And Umno leaders who support this party have betrayed Umno, their race, country and religion," he added in the letter published on his blog.

The former prime minister noted how Umno had once defeated the Malayan Union, struggled to achieve independence and developed the nation.

However, he lamented that Umno has now been reduced to a laughing stock, is rained with insults and rejected by a large number of Malays and non-Malays.

"All of this is because of Najib and his belief that 'Cash is King', which is to govern using corruption," Mahathir reiterated his often repeated allegation.

Najib has denied abusing public funds for personal gain while Putrajaya has accused Mahathir of attempting to topple the prime minister to engineer the political ascension of his son, Mukhriz.

Mukhriz has denied this and filed a defamation suit against the prime minister's press aide Tengku Sharifuddin Tengku Ahmad.

Meanwhile, Mahathir questioned if the elected representatives do not love Umno, which has served the nation, race and religion as well as their families and themselves well.

'Millions reject Najib'

"Don't you feel moved to want to put aside personal interests for the interests of the race and nation?" he asked.

"All that has damaged Umno is done by Najib. As long as he is prime minister, this beloved country of ours cannot be healed.

"Only with Najib's removal can the constitution and laws be enforced once again, and Malaysia will be again respected by the rest of the world," he said.

Mahathir reminded the Umno representatives that the people had elected them to defend their rights and voice out issues on their behalf.

"Now, millions of people reject Najib. Believe me, Umno and BN will lose in the next general election," he said.

Mahathir also listed out the issues concerning Najib and 1MDB, such as the international investigations and the RM2.6 billion donation.

He also noted how, unlike in the past, dissenting voices within Umno were not permitted or silenced.