Prominent members from Malaysia's ruling and opposition parties have joined forces to call for Prime Minister Najib Razak to step down.
Mr Najib has been plagued by corruption allegations, although he denies them and has been officially cleared.
In a joint statement, 58 politicians and activists urged Mr Najib to quit, saying the country would get "worse and worse" under him.
However, Mr Najib's spokesman accused the group of "political opportunism".
The move against Mr Najib was led by influential former PM Mahathir Mohamad, who quit the ruling United Malays National Organisation (Umno) on Monday.
Mr Mahathir called upon all Malaysians to join "in saving Malaysia from the government headed by Najib Razak".
"We must rid ourselves of Najib. If he's allowed to go on, the damage will be worse and worse," he said.
Mr Mahathir was joined by some members of the ruling party, and opposition politicians.
Opposition leader Anwar Ibrahim also expressed his support for the call from prison.
Correspondents say the move from across the political spectrum is remarkable, given the bitter rivalry between Mr Mahathir and Mr Anwar.
Mr Anwar served as deputy prime minister under Mr Mahathir in the 1990s, but tensions grew between the two men and Mr Anwar was eventually sacked and charged with sodomy and corruption - charges he denounced as politically motivated.
Responding to Friday's call for him to resign, Mr Najib's spokesman said it showed his rivals' "political opportunism and desperation".
"There is an existing mechanism to change the government and prime minister. It's called a general election," the spokesman added.
Analysts say that Mr Najib's position appears secure for the moment, as the leader retains control of the party and has forced out cabinet members that threatened his position.
Mr Najib was accused of taking $681m (£479m) from a state investment fund called 1MDB into his personal bank account.
However, the attorney-general's office cleared him in January, saying the money was a personal donation from the Saudi royal family and that most of it had been returned.
The previous attorney-general leading the investigation into the fund was sacked last year.
On Tuesday, the Wall Street Journal said that the total amount of money deposited into Mr Najib's accounts may have in fact exceeded one billion, and that global investigators believed much of it originated from the 1MDB fund.
Mr Najib's office accused the Wall Street Journal of being part of a "politically motivated anti-Najib campaign".