Singapore's government has been put on heightened alert for cyber attacks after people claiming to be from international hacking collective Anonymous defaced several web sites in the city-state and threatened further action.

"Government agencies have been on heightened vigilance and have enhanced the security of their IT systems in response to the declared threats against the government's ICT infrastructure," the Infocommunications Development Authority of Singapore (IDA) said in a statement.

ICT stands for information and communication technology.

The comments came a day after hackers claiming links to Anonymous defaced dozens of websites belonging to Australian businesses and Philippine government agencies.

Several websites in the city-state have also been hacked over the past week, including one belonging to the town council of Prime Minister Lee Hsien Loong's constituency and another belonging to a secondary airport.

IDA said the problems in accessing several Singapore government websites over the weekend were due to technical problems that arose during maintenance on Saturday afternoon. While the glitches have been rectified, people accessing these websites may continue to face intermittent access as maintenance was still ongoing.

On Monday, the website of Singapore's largest newspaper, the pro-government Straits Times, was inaccessible for several hours, three days after a section of its site was successfully attacked by someone claiming to be from Anonymous.

The website of the National Trades Union Congress, closely associated with Singapore's ruling People's Action Party, also appeared to have technical problems, with its eServices down.

"Some users might have had difficulty accessing the straitstimes.com website late last night and some SPH websites today ... The SPH Information Technology Division is investigating the matter," publisher Singapore Press Holdings (SPH) said in response to media queries.

The disruption comes three days after a hacker, who called himself "The Messiah", posted a lengthy message on the paper's online blog page to criticise its report about an internet video by another person claiming to be part of Anonymous.

That person, who wore one of the Guy Fawkes masks that have come to symbolise the group, had threatened to attack Singapore government websites to protest against new licensing rules on news websites.

English Catholic traitor Guy Fawkes was the best-known conspirator in a 17th-century plot to blow up the country's parliament. – Reuters