"Perhaps from the complaints being made by Malaysians about Malaysia one might say there is something rotten in the state of Malaysia," Dr Mahathir, 89, wrote in his blog earlier this month.

And a few days later the man who oversaw Malaysia's development into one of the world's most successful new economies had some blunt advice for current Prime Minister Najib Razak, amid growing political uncertainty in Kuala Lumpur.

"If you don't perform and people say you're no good, please resign," Dr Mahathir said, adding the government is in denial about its problems.

Opposition leader Anwar Ibrahim, the prime minister's biggest political threat, is now behind bars serving a five-year sentence on a rarely used sodomy charge that many Malaysians saw as politically motivated.

But Mr Najib is facing mounting scrutiny and criticisms from his political opponents, including for his use of a draconian Sedition Act to stifle dissent and his oversight of a sovereign venture fund that has lost billions of dollars.

Struggling to hold the support of a Muslim-Malay heartland that has elected his United Malays National Organisation in every election for 58 years, Mr Najib has backed away from promises he made when he took power in 2009 to bolster democracy,

"People are beginning to doubt whether he (Mr Najib) is the sort of leader who can address Malaysia's problems," said Wan Saiful Wan Jan, head of Malaysian think tank IDEAS.

Analysts say the jailing of Mr Anwar could backfire on Mr Najib, whose approval rating is near its lowest level since taking office.

They say the prime minister's enemies in UMNO may try to topple him now that the country's three-party opposition coalition, without Mr Anwar's leadership, faces deep divisions over race and religious policies and may struggle to stay together.

Mr Najib's wife drew fresh scorn on social media this week when she complained about having to pay the equivalent of $425 for house calls by hairstylists.

Questions are being asked about the wealth of Mr Najib's family and the alleged luxury tastes of his wife Rosmah Mansor, who is known for her buying sprees in the world's capitals, while Malaysia's minimum monthly wage is the equivalent of $322.

"Is this woman real? Some families have to live on what she pays to have her hair dyed," one Facebook user said.

Amid growing political uncertainty in Kuala Lumpur, Mr Najib's office insisted his family's lifestyle was not unusual for a person of the "prime minister's position, responsibilities and legacy (of) family assets".

But much larger sums are at stake when it comes to the sovereign fund 1Malaysia Development Berhad, which Mr Najib launched. It is more than  $15 billion in debt and is emerging as a potential serious contingent liability to the government's finances, analysts say. Fears the fund could collapse have rattled Malaysia's financial system.

Mr Najib is hitting back hard at the attempts to undermine his leadership, saying that since 2009 he has improved the lives of Malaysians, fought corruption, reduced poverty, called for a global movement of moderates to combat extremism, improved relations with other nations and propelled Malaysia into the 21^st century.

"Unfortunately the prime minister's political opponents, unwilling to accept his record or the facts, continue to try to undermine him with baseless smears and rumours for pure political gain," a government spokesperson said.

The prime minister's woes come as Malaysia's economy faces a mountain of debt and slumping revenues from oil and gas exports which account for a third of government revenue.

The son of a Malaysian founding father and a British-educated Anglophile, Mr Najib is a savvy political survivor and cannot be easily written off. But analysts are concerned he will be distracted from Malaysia's role this year as chair of the Association of South-East Asian Nations when the ASEAN Economic Community is set to become a reality and when the country has a non-permanent seat on the UN Security Council.

Dr Mahathir, a man known for his vindictive streak, claimed in his blog there were too many complaints about the government to mention. "But not to worry. We will get used to the smell," he wrote.

with agencies