The announcement was swiftly condemned by Anwar's party as a "politically motivated threat" aimed at silencing opposition claims that last Sunday's hard-fought elections were stolen by the ruling coalition.
Vowing to "never surrender" as he addressed a sea of supporters at a rally in a Kuala Lumpur suburb, Anwar late yesterday announced that a series of protest gatherings would be held around the country.
Rafizi Ramli, an official from his party, said two rallies were planned for the weekend in northern states including Anwar's home state of Penang, with another two early next week on the east coast and in the south.
"We will go to every corner of this country," Anwar declared, prompting roars from the multiracial crowd, who filled a stadium and its football field and spilled out in surrounding neighbourhoods.
"We will continue to struggle and we will never surrender!"
Hisan Hamzah, police chief of the state of Selangor where the rally took place, told AFP he may pursue sedition charges against most of the 33 speakers at the rally. He would not confirm whether Anwar would be among them.
"This illegal police investigation is clearly intended to divert attention from the massive electoral fraud and irregularities that are being highlighted by Pakatan Rakyat (People's Pact)," a statement by Anwar's party said, using the name of the three-party opposition alliance.
The huge turnout and the charismatic Anwar's call for similar rallies across the country upped the ante in an opposition campaign to paint the elections as a fraudulent victory for the coalition that has ruled Malaysia for 56 years.
Najib has denied the allegations and urged opponents to accept the election result gracefully.