Former prime minister Dr Mahathir Mohamad today urged Prime Minister Najib Abdul Razak to sue American business paper The Wall Street Journal over the latter's latest claim that more than US$1 billion was transferred into Najib's personal bank accounts.

If Najib fails to do so, then it would only show that the WSJ report 'must have some truth,' Mahathir asserted.

"If it is not true, then the PM should take action to sue them for false reporting.

"But if the PM doesn't sue them, (when) they can be sued in their own countries, then there must be some truth to what was said, " he told reporters at Proton headquarters in Selangor.

The WSJ had put forward fresh allegations today that the sum deposited into Najib's personal bank accounts totalled more than US$1 billion .

This is allegedly inclusive of the US$681 million (RM2.6 billion) deposit, which Najib and Malaysian authorities have identified as a political donation.

However, the WSJ report does not detail how the rest of the US$1 billion made its way into the prime minister's bank accounts, nor where it came from.

Citing sources, it also claimed that most of the US$1 billion originated from 1MDB, and not from Saudi Arabia.

Ever since the WSJ alleged that an amount of USD$ 700 million was transferred into Najib's personal account, Najib has not filed a legal lawsuit against the paper.

Najib has repeatedly denied allegations that he received money from 1MDB, and has denounced WSJ's reports as malicious and false.

Attorney-general Mohamed Apandi Ali has also cleared the prime minister of any criminal wrongdoing in regard to the RM2.6 billion donation, as well as the RM42 million from SRC International Sdn Bhd.

1MDB is currently being investigated for alleged corruption in a number of countries, including Switzerland , Singapore, Hong Kong, and the US.