Corruption watchdog Transparency International has called on the powerful head of a Malaysian state to step aside after a video purportedly linking him to abuse of power went viral online.
But the man at the centre of the allegations, Sarawak's state chief Taib Mahmud, dismissed the video as "naughty" and a possible attempt to smear him.
The clip produced by London-based NGO Global Witness allegedly depicts a "sting", in which a person posing as a foreign businessman is seen negotiating with cousins and associates of Taib. The video has received more than 200,000 views since it was posted on Tuesday and sparked a flood of online postings calling for Taib's arrest.
Taib, 76, has headed resource-rich Sarawak on Borneo island as chief minister since 1981 and has for years faced - and denied - allegations of large-scale corruption and nepotism.
"I saw the so-called proof. Could it not be someone trying to promote themselves to become an agent to get favours from me?" he said in comments that were also uploaded on YouTube.
"I think it is a bit naughty of them for using their big power to blacken my name."
People in the clandestinely shot 16-minute Global Witness video are shown explaining how they make huge profits selling land titles issued by Taib, thus circumventing taxes and Malaysian law, the NGO said.
Neither the identities of the people shown, nor Global Witness' account, could be confirmed. The NGO campaigns against corruption and conflict related to natural resources.
Authorities should launch a full investigation of the video, Josie Fernandez, secretary-general of Transparency International's Malaysian chapter, said in Kuala Lumpur.
She also urged the Malaysian Anti-Corruption Commission (MACC) to speed up an investigation into Taib that the agency said it had launched two years ago.
The Swiss-based Bruno Manser Fund released a report in September alleging Taib had amassed an estimated US$15 billion fortune, which would make him Malaysia's richest man and one of the world's wealthiest.
Activists accuse Taib and his family of massive graft in awarding timber concessions and other contracts, and of rapacious development that has seen rain forests felled, questionable dams built and tribal groups uprooted.
Taib says the state needs to be developed.
The MACC's director of investigation, Mustafar Ali, said the Taib probe was continuing.
"With the new evidence that has emerged, the MACC will act accordingly," he said.