Muhyiddin, who was removed as deputy prime minister last July, has been waging a public campaign along with Mukhriz criticising Najib over allegations of abuse of public funds by state investor 1Malaysia Development Berhad (1MDB).

Mukhriz was forced to quit as the chief minister of the northern Kedah state in February.

Both were previously suspended from the party.

Shafie Apdal, a former cabinet minister, who was dismissed last year for colluding with Muhyiddin, has also been suspended, local media said.

Muhyiddin had repeatedly lent weight to mounting public calls for Najib to answer allegations that hundreds of millions of dollars of 1MDB money had gone missing in complex overseas transactions that have never been fully explained.

Both 1MDB and Najib vehemently deny wrongdoing.

In April, a Malaysian parliamentary committee said at least US$4.2 billion in questionable overseas money transfers were made by 1MDB.

Najib was plunged into the crisis last year when it was revealed that US$681 million in transfers were made to his personal bank accounts in 2013. He says they were “personal donations” from the Saudi royal family.

In May, Swiss financial regulators approved the dissolution of Switzerland-based BSI Bank over “serious breaches” of money-laundering regulations in its dealings with 1MDB.

Najib has faced calls to resign but he has tightened his grip on the ruling party and thwarted domestic investigations. His position is not seen as under imminent threat.

Authorities in a half-dozen countries are investigating 1MDB money flows, however, and Switzerland and Singapore have frozen millions of dollars in assets.