Najib Razak
The spotlight is fixed on Malaysian Prime Minister Najib Razak as the 1MDB row deepens Olivia Harris/Reuters

Total banks deposits into personal accounts of Malaysian Prime Minister Najib Razak allegedly topped $1 billion (£716 million) – hundreds of millions more than previously identified by investigations into state development fund 1Malaysia Development Berhad (1MDB), according to a Wall Street Journal (WSJ) report.

The damning revelations in an ever-deepening scandal triggered the resignation of former prime minister Mahathir Mohamad from the ruling United Malays National Organisation (UMNO) party. A strong critic of his embattled successor Razak, Mohamad said he felt "ashamed" to be associated with "a party that is seen as supporting corruption".

In January, Malaysia's attorney general Mohamed Apandi Ali cleared Razak of wrongdoing after ruling that the previously reported sum of $681m transferred into the prime minister's account in 2013 was a legal donation from the Saudi royal family. While it is believed that most of that money was sent back to the House of Saud, investigators in two countries now suspect that the money actually came from 1MDB to begin with.

Investigators believe that the funds were able to flow through an intricate network of multinational transactions with the assistance of two former officials from Abu Dhabi, with which 1MDB has close links. The latest report prompted 1MDB to hit back at the WSJ, claiming that it had failed to uphold "basic journalistic standards", according to reports in Malaysian media.

Earlier this month, 1MDB said that it had not paid any money into Razak's personal accounts. On 1 March, the state fund blasted the latest allegations and said: "Not once has the publication offered any conclusive evidence to support its claims, with the only justification for their continued attacks being information that they claim to have obtained from unnamed and anonymous sources.

"This reliance on anonymous sources, who may or may not exist, betrays a lack of basic journalistic standards on the part of the Wall Street Journal and the fact that the publication has lost all semblance of balanced reporting," it added.

Razak's office declined to comment on whether transfers made into his accounts topped $1bn. The Malaysian leader founded the state fund when he came to office in 2009 to pump money into projects of national importance.

The spiralling scandal has led to investigations being opened in the US, Switzerland, Hong Kong, Singapore and Abu Dhabi, as well as Malaysia, according to the WSJ.