Former premier Dr Mahathir Mohamad today refuted claims that he lodged a report to the United States alleging Prime Minister Najib Abdul Razak abused his power and embezzled government funds.

This comes after the US Department of Justice (DOJ) filed lawsuits seeking to seize US$1 billion of assets purchased using funds allegedly stolen from 1MDB.

"I did not make any reports. But even if I did, wrong is wrong," he said.

"Umno leaders' attempts to say that Najib is not guilty will not prove his innocence. They can accuse, condemn and insult me, what is wrong remains wrong," he said in a blog post.

The DOJ lawsuits is a result of ongoing investigations by the US Federal Bureau of Investigation (FBI) and the DOJ as part of the Kleptocracy Assets Recovery Initiative (Kari).

According to the New York Times, former Umno division leader Khairuddin Abu Hassan was due to meet with the FBI last September, when he was stopped from leaving the country.

Khairuddin lodged multiple reports on 1MDB with various foreign agencies, before he was arrested for sabotaging the economy and detained under the Security Offences (Special Measures) Act.

He claimed trial for the sabotage charge and was released on bail after the court found the offences did not fall under Sosma.

Mahathir said the DOJ court filings' detailed account of how 1MDB funds were allegedly embezzled has placed Malaysia as the global capital of kleptocracy, and yet Umno members remain unabashed.

"Najib's name may not be stated but everyone knows that 'Malaysian Official 1' is Najib. Only stupid people cannot recognise that it is referring to Najib, and only they can accept Najib as their leader.

"Umno leaders should stop lying to themselves. You know Najib is guilty, and you know Najib is not qualified to be prime minister," he said.

He said that Umno leaders who continue to be in denial are abetting a crime.

Najib has consistently denied wrongdoing and said he has never abused public funds for personal need.

'Malaysian Official 1' was described in the filings as a high-ranking Malaysian public officer who had a high position in 1MDB and is a relative of Naib's stepson Riza Aziz.

Riza, his friend and businessman Jho Low and two Abu Dhabi businessmen were named in the DOJ filings.

When asked why 'Malaysian Official 1' was not named, US attorney-general Loretta Lynch said the lawsuits only names those it needs to name to meet the objective of seizing the assets.

According to the lawsuits, 'Malaysians Official 1' received US$731 million of funds originating from 1MDB.

The transactions matched that described by attorney-general Mohamed Apandi Ali when he cleared Najib of wrongdoing in the RM2.6 billion found in the PM's bank account.

Speaking after the Umno supreme council last week, Najib said the council took note of the fact that 'Malaysian Official 1' was mentioned in the DOJ’s lawsuits.

"We noticed that, we noted that and the position has been explained to the public," Najib said.

He had earlier also called on those named in the lawsuits to clear their names, and assured that the government is committed to good governance.