A Malaysian court upheld on Tuesday the acquittal of jailed former prime minister Najib Razak on an audit tampering charge in the investigation into corruption at the 1MDB state wealth fund.

Najib is serving a 12-year prison term on other graft charges related to the 1 Malaysia Development Berhad financial scandal.

The plundering of the fund led to investigations around the world, including in the United States, Switzerland and Singapore, into the use of their financial systems to launder money.

But Malaysia's Court of Appeal struck out the appeal by state prosecutors against the acquittal of the audit tampering charge after prosecutors did not submit documents in time, Najib's lawyer Mohamed Shafee Abdullah told AFP.

"In this case, the prosecution evidently found no grounds for appeal, resulting in no petition being filed," he said in a statement.

Najib, the 70-year-old leader of Malaysia for nine years until 2018, was acquitted in March after a Kuala Lumpur High Court judge ruled prosecutors failed to provide sufficient evidence that he had tampered with an audit report on scandal-racked 1MDB.

That charge focused on allegations that Najib ordered a report by the government's official audit body on the 1MDB sovereign wealth fund to be altered in February 2016.

Najib's co-accused, former 1MDB chief Arul Kanda Kandasamy, was also acquitted.

The former Malaysian premier's acquittal from the tampering charge does not affect his current jail sentence and he faces dozens more charges that could lengthen that term.

Najib's wife Rosmah Mansor was found guilty of graft in 2022 and sentenced to 10 years in prison.

She remains on bail pending an appeal.