Najib was summoned by the MACC to give a statement over claims surrounding SRC International, an energy company that was originally a subsidiary of 1MDB, and forms just one part of the wide-ranging probe into the scandal.
Swarmed by reporters, Najib looked calm and smiled as he was escorted into the agency's building.
"The Prime Minister has agreed to the formation of 1MDB Task Force to carry out detailed investigations, detection and seizure of assets, as well as prosecution against individuals who commit any criminal offence in the management of 1MDB", the statement said.
In her first statement since Najib's long-ruling coalition was ousted in May 9 elections, Rosmah Mansor said authorities conducting a corruption and money-laundering investigation should avoid a "premature public trial" of her family.
Mahathir Mohamad, the new prime minister, said the task force would meet for the first time Tuesday and investigate crimes committed in relation to 1Malaysia Development Berhad (1MDB), which Najib founded in 2009 as a sovereign wealth fund to support economic development in the country.
On Tuesday, the US Department of Justice said it would continue to pursue investigations related to 1MDB, adding that it was looking forward to working with Malaysian authorities on the matter.
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A new attorney general in 2016 cleared Najib of wrongdoing, saying a particular transfer of $681 million was a political donation from the Saudi royal family and that most of it was returned.
Addressing loyalists in his home state of Pahang on Sunday, Najib declared: "I did not steal from the people".
On May 18, police seized 284 boxes filled with designer handbags, watches, jewellery and cash in various currencies from three condominiums at Pavilion Residences in Kuala Lumpur.
Mahathir spoke on Monday to civil servants and other officials outside the Prime Minister's Office, vowing to root out corruption. Instead we were accused of bringing down the country; we were accused of being traitors.
The embattled former leader had been ordered by the MACC to explain a suspicious transfer of RM42 million (US$10.6 million) from SRC into his bank account.
As these funds were moved through Malaysian, rather than foreign, financial institutions it was easier for MACC investigators to establish the money trail.