The son of former Malaysian Prime Minister Mahathir Mohamad has resigned as a state chief minister, saying he was ousted because of his criticism of Prime Minister Najib Razak over a $700 million financial scandal.

Mukhriz Mahathir says he had lost majority support in the northern Kedah state assembly following a party bid to remove him.

He warned Thursday the ruling Malay party was now at "its weakest point," tainted by scandal-ridden state investment fund 1MDB and more than $700 million that was channeled into Najib's accounts.

Mahathir has been leading calls for Najib to step down, and Mukriz's ouster was seen as a continuing purge of critics in Najib's government. The attorney-general has said he would not prosecute Najib as most of the money was a private donation.