A Malaysian opposition party leader urged Prime Minister Najib Razak to step down after the US prosecutors filed lawsuits over the transactions at scandal-plagued state-owned fund 1Malaysia Development Berhad (1MDB).

The president of Parti Keadilan Rakyat (PKR), Dr. Wan Azizah Wan Ismail, said the government also should set up an independent commission in order to investigate the claims made in the civil suits filed in California on Wednesday.

"I believe the Malaysian people want Datuk Seri Najib to go on leave as prime minister so as not to create the perception of abuse of power or process to halt or hinder a full and transparent investigation on this very serious issue," Dr. Wan Azizah said in a statement on Thursday.

The US Justice Department seized more than US$1 billion (S$1.35 billion) worth of assets, including luxury real estate and a jet which apparently was purchased from 1MDB money.

The court filings made "thinly veiled references" to Najib as the US declared that billions of dollars were "siphoned off by Mr Najib's stepson, a family friend and other officials".