Apart from one or two dissenting voices, Umno has been supportive of its president Najib Abdul Razak in the face of numerous allegations against him.

And Dr Mahathir Mohamad has diagnosed the problem.

According to him, Umno members are stuffed with "animal feed (dedak)" and this in turn made them silent.

"It is said that animal feed was stuffed into the mouths of party members to keep them silent.

"There are even party members who admitted to receiving as much as RM1 million and RM2 million to shut their mouths about the crime that is clearly happening.

"They will just agree to everything," Mahathir said in his latest blog post.

The term "dedak" is often used to refer to people who have received benefits from certain quarters and have therefore become compliant to them.

Mahathir said it is for the same reason that a vote of no-confidence against the prime minister cannot be put into motion.

"Normally, when a leader abuses power, the Federal Constitution gives MPs the right to a no-confidence vote in the House.

"But because of animal feed and various pressures, no Umno and BN MPs, apart two from Umno, would dare to support a no-confidence vote if it is tabled," he said.

Mahathir claimed that Umno division leaders were also silent after seeing other leaders being arrested and charged after questioning the prime minister.

Likewise, he said Umno branch leaders were also sacked for critcising Najib.

"Regardless of Najib's wrongdoings, regardless that billions in government funds had gone missing, regardless of Najib suddenly possessing billions in his personal bank accounts which the source cannot be explained, BN MPs and Umno division leaders remained silent," he said.

Mahahir also lamented the loss of freedom of speech under Najib's government, claiming that the people's right to speak was under siege.

"The print and electronic media is fully controlled by Najib and no longer report the truth.

"Information is twisted that they do no reflect the real facts. Attempts are made to block the alternative media," he said.

Mahathir had accused Najib of corruption over the deposits of billions in his personal bank accounts, claiming that it is linked to state-owned 1MDB.

However, the prime minister denied this, and stressed that he had never taken public funds for personal gain.

He said the money in his personal bank accounts was an Arab "donation".

Attorney-general Mohamed Apandi Ali has also cleared the prime minister of any wrongdoing.