United States' prosecutors have considered the possibility of charging Najib or his associates, however, they would prefer Malaysia be the one to file criminal charges against any Malaysian official.
"That's how its supposed to work," a US law enforcement official said.
This comes as US investigators have accelerated their probe into the 1MDB sovereign wealth fund set up by former Malaysian prime minister Najib Abdul Razak and are exchanging more evidence with Malaysian authorities since Najib lost last month's election, three sources with direct knowledge of the probe said.
At least six countries, including Malaysia, the United States and Switzerland, are investigating accusations that Najib and associates pocketed part of $4.5 billion allegedly stolen from the state-run investment fund, 1Malaysia Development Berhad.
The Federal Bureau of Investigation is confident that Malaysia's new government is more willing to cooperate, whereas US authorities saw Najib's as actively obstructing the investigation, according to two people with direct knowledge of the investigation.
Najib has retained former US attorney-general John Ashcroft and the firm of New York trial lawyer David Boies to represent him in connection with the US investigations, a source familiar with Najib's legal team said.
In a series of asset seizures last year, US prosecutors alleged in court papers that some of the money stolen from 1MDB was placed into the account of an individual identified as "Malaysian Official 1."
Since Najib's election defeat, Malaysia's new government has been scrambling to recover billions of dollars allegedly syphoned from 1MDB.
It is considering asking the US government to get investment bank Goldman Sachs to return nearly $600 million in fees it earned from bonds raised for the sovereign wealth fund, two sources familiar with the matter told Reuters on Friday.
No formal request has yet been made but top officials are actively discussing the plan within the government, they said.
Najib's successor, Prime Minister Dr Mahathir Mohamad, said Malaysia was also seeking to arrest financier Low Taek Jho, a central figure in the scandal who advised on investments and negotiated deals for 1MDB.