KUALA LUMPUR • Questions surrounding a troubled Malaysian state investment fund and missing money in the Middle East have widened to include as much as US$1 billion (S$1.4 billion) more, according to the Wall Street Journal (WSJ).

Last week, the US-based newspaper said officials in Abu Dhabi were trying to understand why a US$1.4 billion transfer that the fund - 1Malaysia Development Berhad (1MDB) - said it made to a counterpart in the Gulf emirate was not received.

In another report published yesterday, it said those officials are now questioning a further US$993 million that 1MDB reported it paid to the Abu Dhabi fund, the International Petroleum Investment Company (IPIC), but which also appears to be largely missing.

WSJ said this was according to people familiar with the matter.

The report said that in 2012, the Abu Dhabi fund agreed to guarantee US$3.5 billion in bonds issued by 1MDB for the purchase of some power plants.

In return, IPIC was given options to buy a stake in those power assets. But both sides agreed to end the deal last year, with 1MDB agreeing to buy back the options for an undisclosed price, said WSJ.

1MDB dismissed WSJ's earlier report on the missing US$1.4 billion payment, calling it "biased and sensationalist". It said in a statement on Sept 9 that its audited financial statements had clearly described the amount and purpose of the payments.

The state investment firm repeated those points when it dismissed the "malicious insinuations" of the latest WSJ report.

Set up by Malaysian Prime Minister Najib Razak in 2009 to invest in Malaysia's economy, 1MDB is now struggling to repay more than US$11 billion worth of debts.

In July, WSJ reported that a Malaysian government investigation found almost US$700 million entered the Prime Minister's private accounts through entities linked to 1MDB ahead of an election in 2013.

But Malaysia's anti-corruption body said last month that the funds were not from 1MDB and were a political donation from a donor in the Middle East.