Prime Minister Najib Abdul Razak today assured the government will take action against whistleblower site Sarawak Report over its allegations against 1MDB.

He said this will be done after Thai authorities conclude their investigation on Xavier Andre Justo ( photo ) who was arrested in Thailand on Monday.

"We have to wait for the report by the Thai authorities. I've been made to understand that they will be informing the Malaysian police.

"If we get the admission (by Justo) and clear proof submitted by the Thai government through the police, the Malaysian government will make the appropriate decision," he told a press conference in Kuala Lumpur after chairing the Umno supreme council meeting.

Najib stressed that he did not want to precede the official report by the Thai authorities and told the media today that both Inspector-General of Police Khalid Abu Bakar and Home Minister Ahmad Zahid Hamidi were awaiting the report from the Thai government.

Justo, a former PetroSaudi International (PSI) staff, is accused of blackmailing his former employer using information he allegedly stole from the company.

The same leaked information, which also contained PSI's communications with 1MDB, was passed to Sarawak Report.

Sarawak Report subsequently used this information to allege that US$700 million in a joint venture between PSI and 1MDB was siphoned out to a company owned by billionaire Jho Low, who is close to the prime minister's family.

'Gov't views corruption seriously'

On a separate matter, Najib told the same press conference that the government viewed corruption allegations in Mara's purchase of property in Australia seriously.

He promised that the government will ensure a transparent investigation into the matter.

Najib also said that the two Mara Inc executives - who were incriminated by Australian newspaper The Age in the controversial purchase of the Dudley International House property - should not be subject to trial by the media, nor trial by social media.

"We have to investigate whether what they did was against the law or otherwise. We cannot take action based on suspicion or trial by the media or trial by social media.

"(It) must be decided by the process of the rule of law. You are deemed to be innocent until proven guilty, not guilty until proven innocent," he said.