Najib Razak

The rally was organized by Bersih, a coalition of nongovernment organizations that want to reform and clean up Malaysia's electoral process.

Bersih means "clean" in Malay, and Saturday's rally was the fifth phase of street protests the group has undertaken. Bersih supporters wear yellow T-shirts.

A statement from the Prime Minister's office dismissed the protest as the rantings of a politically ineffective and anti-democratic opposition movement.

The crowds were undeterred by a heavy police presence after authorities declared the rally illegal, blocked the organizer's website and banned yellow attire and the logo of Bersih, the coalition for clean and fair elections that's behind the weekend rallies.

Najib has been fighting for political survival after leaked documents in July showed he received some $700 million in his private accounts from entities linked to indebted state fund 1MDB. 

Najib is under increasing pressure over leaked confidential documents that allegedly show the money, from state investment fund 1MDB, went into his personal accounts.

Najib announced over national television that his deputy Muhyiddin Yassin will be replaced by Ahmad Zahid Hamidi, a Cabinet member who will also retain his home minister portfolio. Earlier Tuesday, the government announced it had terminated the services of Attorney General Abdul Gani Patail.

 This represents the first time a Malaysian leader has faced criminal allegations.

The country's attorney general confirmed late Saturday that he had received documents from an official investigation that made the link between Prime Minister Najib Razak and the investment fund 1MDB. 

The existence of the documents was first reported by The Wall Street Journal's Asia edition on Friday, showing some $700 million were wired from entities linked to the fund into Najib's accounts.

The documents sent to the attorney general pave the way for possible criminal charges.