A motor cyclist rides past a hoarding at the construction site of the 1 Malaysia Development Berhad (1MDB) flagship Tun Razak Exchange in Kuala Lumpur on July 8, 2015

Malaysian authorities said they had blocked a UK-based website that had published corruption allegations against Prime Minister Najib Razak, but the portal vowed Monday to press on with its exposes.

The Sarawak Report website has recently published reports alleging involving Najib and debt-laden state investment vehicle 1Malaysia Development Bhd (1MDB).

The Malaysian Communications and Multimedia Commission announced on Sunday it had blocked the site for carrying "unsubstantiated content".

Without specifying which content was deemed unacceptable, the commission warned the reports could have major consequences.

"Such content could disrupt peace and order, and in the bigger picture could destabilise the nation and the economy," the statement said.

The website, run by Clare Rewcastle Brown, a former BBC journalist and sister-in-law to ex-British prime minister Gordon Brown, issued a defiant statement in response to the blocking.

"This is a blatant attempt to censor our exposures of major corruption through the development fund 1MDB," said a statement posted on the Sarawak Report's Facebook page.

"Sarawak Report will not be impeded in any way by this action in bringing out future information as and when its investigations deliver further evidence."

The Sarawak Report, which can still be accessed by overseas servers, carried a report early this month alleging it had evidence that Najib had received $700 million from entities involved with 1MDB.

The Wall Street Journal also ran a story alleging that a probe into 1MDB had found hundreds of millions of dollars transferred to Najib's personal bank accounts.

1MDB has denied any wrong doing and Najib has dismissed the allegations as "political sabotage" and an attempt to undermine his leadership.

Both Najib and 1MDB have also said that previously leaked documents had "reportedly" been tampered with, and that the documents cited by the WSJ had not been verified

1MDB was launched in 2009 by Najib, who still chairs its advisory board. Critics say it has been opaque in explaining its dealings.

It is reeling under an estimated $11 billion debt, which has weighed on the ringgit currency amid allegations of mismanagement and murky overseas transactions.

The Centre for Independent Journalism, Malaysia, (CIJ), called Monday on the country's internet regulator to "respect the right to freedom of expression and to cease its blocking of Sarawak Report".

"CIJ renews its calls for a focus on investigating the actual issues at hand, and rejects further regulation and censorship on the internet as a way to manage the issue," it said.