Malaysia's prime minister is under mounting scrutiny for cracking down on opponents, troubles in a strategic development fund and questions about his family assets - with even ruling-party conservatives questioning his leadership.

Prime Minister Najib Razak, 61, took the helm of the multiethnic country's long-ruling government in 2009, promising to soothe racial tensions and bolster democracy.

But he is under fire from progressives for abandoning his pledges and from ruling-party hardliners over 1MDB - a government-owned development company he launched that is believed to be in precarious condition.