Former Malaysian leader Mahathir Mohamad has called for an immediate vote of no-confidence against Prime Minister Najib Razak, saying Najib has made members of parliament beholden to him by giving them lucrative government posts.

Najib, under growing pressure over allegations of graft and financial mismanagement at debt-laden state fund 1Malaysia Development Bhd (1MDB), in August sacked his deputy, Muhyiddin Yassin, replaced the country's attorney general and transferred officers involved in the 1MDB investigation.

Mahathir, Malaysia's longest-serving prime minister, has become Najib's fiercest critic and withdrew support for him last year after the ruling Barisan Nasional (BN) coalition's poor showing in 2013 elections.

"A vote of non-confidence is necessary now because Najib has made BN members of parliament beholden to him by giving them lucrative posts in the government," Mahathir said in a post published on his blog late Thursday.

"Even those who had come to me complaining about Najib's administration before, upon being given posts in his government, have now changed their stand."

The 90-year-old, who was once Najib's patron and remains highly influential in the country, has called for the prime minister to step down over the 1MDB furor.