A Malaysian court acquitted jailed former prime minister Najib Razak of a corruption charge on Friday but he will continue to serve a 12-year prison term from another case.

High Court judge Mohamed Zaini Mazlan said state prosecutors failed to provide sufficient evidence to prove their case that Najib tampered with an official audit report on scandal-wracked state fund 1MDB for his benefit.

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

"The first accused (Arul Kanda) is discharged and acquitted from the charge. The second accused (Najib) is discharged and acquitted against the charge made against him," the judge said in court.

The charge dismissed Friday -- which carried up to 20 years in jail on conviction -- focused on allegations that Najib used his position to order a report on the 1MDB sovereign wealth fund by the government's official audit body to be altered in February 2016.

The changes were aimed at exonerating him from any criminal liability, according to the charge.

He was allegedly assisted by Arul Kanda, who was president and chief executive of the fund at the time.

Najib, 69, was brought to court Friday from Kajang Prison, where he is currently serving a 12-year jail sentence for abuse of power, money laundering and criminal breach of trust over the transfer of 42 million ringgit ($10.1 million) from former 1MDB unit SRC International to his personal bank account.

Malaysia's highest court dismissed his final appeal on that case in August last year and ordered him to immediately begin serving his sentence.

His acquittal from the tampering charge does not affect the current sentence.

Friday's acquittal eased the pressure on Najib, but the former leader still faces dozens more charges, which could lengthen his time in jail.

Most of the charges are related to his alleged role in the 1MDB financial scandal, which led to investigations around the world -- including in the US, Switzerland and Singapore -- for the use of their financial systems to launder stolen funds.

Najib's lawyer Muhammad Shafee Abdullah told reporters outside the court that the former prime minister was "relieved" following his acquittal.

Allegations that billions of dollars were pilfered from investment vehicle One Malaysia Development Berhad (1MDB) and used to buy everything from a super-yacht to artworks played a major role in prompting voters to oust Najib and the long-ruling United Malays National Organisation party in 2018 elections.

Najib, the UK-educated son of one of Malaysia's founding fathers, had been groomed for the prime minister's post from a young age.

He set up 1MDB after coming to power in 2009 to bolster economic development, but the fund amassed billions of dollars in debt.