The Malaysian Insider has been a key player in the growth of plucky online news sites that have rapidly gained a following over the past decade by reporting on official malfeasance and corruption filling a void left by pro-government traditional media.

Last month Malaysia's government began blocking access to the site after it published a story on corruption allegations swirling around Najib.

The website's owner The Edge Media Group said in a statement that it had been in negotiations to sell the loss-making portal but that talks broke down in the wake of the government block.

"We believe the recent problems TMI had with (the Malaysian government) had made it more difficult for a sale to be concluded" it said adding that it had no choice but to close the site.

The news will fuel further fears for democratic space and media freedoms under Najib.

Najib 62 has been under pressure for a year over allegations that billions of dollars were pilfered from a state fund he oversees and for his own admitted acceptance of a mysterious $681 million sum.

As calls for his ouster mounted Najib has purged critics from his government and taken other steps that have stalled investigations.

Najib's government also banned publication of The Edge's print newspaper last year. A court lifted the suspension two months later.

The Malaysian Insider's blocking last month was criticised by media and rights groups with Human Rights Watch calling it a "blatant and outrageous breach" of media freedoms and accusing Najib of "tightening the noose of censorship and control."

Political analysts say Najib has so far largely neutralised pressure to step down by using the long-ruling United Malays National Organisation's (UMNO) grip on Malaysia's police and other key institutions.

But authorities in several countries are investigating money flows related to the scandal with Switzerland and Singapore announcing previously that they had frozen a range of bank accounts. US authorities are reported to be investigating.

Two Australian television journalists were detained overnight Saturday after approaching Najib to question him over the graft allegations.

They have been released but remain barred from leaving as they await possible charges their lawyer said.