Activist group Anonymous hacked a Singapore newspaper website Friday over Internet freedom in the city-state, where government agencies are now reportedly on alert for wider cyber attacks.

The website of the pro-government Straits Times was hacked early in the day by apparent members of the group, which is opposing recently introduced licensing rules for news websites in Singapore on censorship grounds.

The attackers, using the name "Messiah", took over the blog of a Straits Times journalist, saying she had distorted "our words and intentions" in a report on the group's threat a day earlier to "wage war" on the Singapore government.

"We oppose any form of Internet censorship among other things," said a post on the journalist's hacked blog, which is part of the newspaper's website and has been taken offline.

The hackers urged the journalist to apologise within 48 hours "to the citizens of Singapore for trying to mislead them".

If she fails to apologise, "then we expect her resignation", the hacker said in the hacked account, still visible in online caches.

"If those demands are met we will be on our way. But in the event our demands are not met in the next 48 hours, we will place you in our 'to do' list and next time you wont (sic) be let off this easy."

Asian media giant Singapore Press Holdings, which publishes the newspaper, said: "We have made a police report, and the police are investigating."

The attack on the Straits Times followed a post on the video-sharing site YouTube on Thursday in which a person claiming to speak for Anonymous warned the group would cause Singapore to suffer financial losses from "aggressive cyber intrusion".

Singapore, which has been governed by the same party for 54 years and strictly regulates the traditional media, is Southeast Asia's financial centre and hosts the regional headquarters of many global companies.

"We demand you reconsider the regulations of your (Internet) framework or we will be forced to go to war with you," a male voice said, addressing the government, as a person hiding behind a mask appeared in the YouTube clip.

The original video has been taken down, but has been copied by other users and can still be viewed online.

Reacting to the YouTube clip, Singapore's Infocomm Development Authority said: "We are aware of the video, and the police are investigating into the matter."

The Straits Times, meanwhile, said it had learned government agencies had been put on alert in Singapore following the initial threat on Thursday.

It said the alert directive came from the Government IT Security Incident Response Team, which was set up to coordinate responses to cyber attacks.

The new rules opposed by the hackers were imposed on June 1 and require annual licensing for news websites with at least 50,000 unique visitors from within Singapore every month.

Websites granted a licence must remove "prohibited content" such as articles that undermine "racial or religious harmony" within 24 hours of being notified by Singapore's media regulator.

The new rules have sparked anger in the city-state's robust blogging and social media community, which has accused the government of failing to carry out a consultation and raised fears the regulations are aimed at muzzling free expression.

Blogs and social media have gained popularity as alternative sources of news and opinion in Singapore, where mainstream newspapers and broadcasters are perceived to be pro-government.

Under Singapore's Internet code, prohibited content includes "material that is objectionable on the grounds of public interest, public morality, public order, public security, national harmony, or is otherwise prohibited by applicable Singapore laws."

Singapore authorities insist the licensing rules do not impinge on Internet freedom.