In this file photo dated Aug 23, 2022, Malaysia's former prime minister Najib Razak (center) greets supporters as he walks out during a break in the trial during an appeal against his corruption conviction over the 1MDB financial scandal, at the federal court in Putrajaya. (PHOTO / AFP)

KUALA LUMPUR — Malaysian prosecutors have not appealed the acquittal of former Prime Minister Najib Razak in a case of audit tampering related to state fund 1MDB, his lawyers said on Tuesday, risking backlash for premier Anwar Ibrahim who has vowed to fight graft.

Anwar is already under pressure from allies and the opposition after his government last week dropped dozens of graft charges against a key ally whose support is essential for the premier to keep his parliamentary majority.

Concerns were raised after he partnered with Najib's corruption-tainted party to form a government and appointed officials accused of graft

Najib, 70, is serving a 12-year jail sentence for another corruption case linked to 1Malaysia Development Berhad (1MDB). He also faces several other graft charges.

READ MORE: Malaysia ex-PM, 1MDB ex-CEO cleared of audit tampering

The attorney-general's chambers was expected to appeal Najib's acquittal earlier this year of a charge of abusing his position as prime minister to amend a government audit into 1MDB .

But Najib's lawyers at Shafee & Co said in a statement, "the prosecution evidently found no grounds for appeal" and did not file the petition.

Najib had pleaded not guilty.

An estimated $4.5 billion was allegedly misappropriated from 1MDB by high-level officials of the fund and their associates between 2009 and 2014, the US Justice Department has alleged.

READ MORE: Malaysia court rejects Najib’s bid to drop 1MDB audit charges

Anwar, who came to power in November last year, had vowed to fight corruption as part of his election campaign. But concerns were raised after he partnered with Najib's corruption-tainted party to form a government and appointed officials accused of graft to senior positions.

Malaysia's Prime Minister Anwar Ibrahim attends the 18th East Asia Summit as part of the 43rd Association of Southeast Asian Nations (ASEAN) Summit in Jakarta on Sept 7, 2023. (PHOTO / AFP)

On Sunday, the Malaysian United Democratic Alliance said it was leaving Anwar's ruling coalition, citing concerns after graft charges were dropped against Ahmad Zahid Hamidi, the country's deputy premier.

In this file photo dated March 14, 2016, a worker walks past a poster of the 1 Malaysia Development Berhad (1MDB) logo on a truck in Kuala Lumpur, Malaysia. (PHOTO / AFP)

Anwar has maintained that the move to drop the case, which triggered a widespread public backlash, was made without his interference.