Ho Kay Tat, head of The Edge media group, was arrested along with Jahabar Sadiq, chief editor of The Malaysian Insider news portal which is owned by The Edge, the portal said.

The latest detentions followed the arrests of scores of people in recent weeks for sedition or for assembly violations related to a series of demonstrations demanding the release of jailed opposition leader Anwar Ibrahim or other anti-government protests.

Three other Malaysian Insider editors had already been arrested on Monday over a seemingly uncontroversial news report involving the Muslim-majority country's royalty.

The Edge, however, has also published a string of reports on the murky dealings of a government-owned investment company whose board is chaired by Prime Minister Najib Razak.

Those reports -- including questions over the whereabouts of huge sums of money -- have stirred public outrage and deeply tarnished Najib's image.

In a statement issued before his arrest, Jahabar said the police actions "appear to go beyond just our reportage" on the story concerning the sultans.

"The Malaysian Insider will continue to report without fear or favor despite these arrests. It is business as usual," he said.

Facing sliding voter support over repressive tactics and corruption in his ruling coalition, Najib promised in 2011 to end the regime's authoritarian ways.

But he made an abrupt u-turn after a further setback in 2013 elections in which the opposition won a majority of votes cast, launching a crackdown on free expression in which dozens of opposition politicians, academics and activists were nabbed last year on sedition and other charges. 

Most spent no more than a few hours in custody before being released.

A new wave of arrests has targeted critics of the February jailing of Anwar.

Anwar was imprisoned for five years on the charge of sodomizing a male aide in 2008, which he says was fabricated by the government to halt the opposition's electoral momentum.

Najib's office did not respond to a request for comment, but the premier said last week that freedom must have limits.

Bridget Welsh, a Malaysia politics analyst with National Taiwan University, said the arrests were a sign of Najib's political weakness, with the premier believed to be under pressure from ruling-party hardliners.

"They are trying to create a climate of fear, silence their critics and divide the opposition," Welsh said.

Police said the latest arrests stem from a Malaysian Insider report last week.

The report said a council of the country's nine figurehead state sultans opposed an Islamic opposition party's proposal for tough sharia criminal punishments.

Authorities have not explained how the report, which the council has claimed is false, could be considered seditious, but Malaysia has strict rules against insulting the sultans.

Senior opposition figure Lim Kit Siang called the recent spate of arrests a reign of "terror" that evoked the coordinated 1987 arrests of 106 activists, opposition politicians, intellectuals and other regime critics.

"The question can be legitimately asked whether the country is seeing a replay of the [1987] dragnet," Lim, who was himself arrested at the time, said in a statement.

That episode was far harsher than the current crackdown.

Like Lim, many of those arrested in 1987 spent more than a year in detention without charge. Historians say the affair marked a key acceleration of authoritarian rule in the country.

Press groups denounced the journalist arrests, saying the apparently innocuous sultan report was no grounds for sedition charges, which are punishable by up to three years in jail.

Malaysia's Center for Independent Journalism and the Southeast Asian Press Alliance, in a joint statement, called the arrests "an assault on media freedom and an act of intimidation" by authorities, and demanded the journalists' immediate release. (+++++)

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