"Online news sites that report regularly on issues relating to Singapore and have significant reach among readers here will require an individual licence," Singapore's Media Development Authority (MDA) said in a statement.
"This will place them on a more consistent regulatory framework with traditional news platforms which are already individually licensed," the media regulator said.
Prosperous and orderly Singapore, a regional base for many multinationals and fund managers, is one of the world's most wired-up cities with most people having broadband access.
It has long maintained strict controls on the media, saying that was necessary to maintain stability in a small, multi-racial country and that media must be held accountable for what they publish.
Lobby group Reporters Without Borders, in its latest report, ranked Singapore 149th globally in terms of press freedom, down 14 places from 2012 and below many of its neighbours.
In 2011, the city-state's tiny opposition made big gains against the long-ruling People's Action Party in parliamentary elections, partly by using the Internet to reach voters.
A survey by the Straits Times newspaper shortly before the vote found 36.3% of people between the ages of 21 and 34 cited the internet as their top source of domestic political news compared with 35.3% who preferred newspapers.
"Will find a way"
The MDA identified sg.news.yahoo.com, a service run by internet giant Yahoo Inc, as among 10 sites that would be affected by the new requirement, based on criteria such as having 50,000 unique visitors from Singapore a month over a period of two months.
Yahoo declined to comment when contacted by Reuters.
"We are not in a position to respond until we receive the actual license conditions for review," the head of its Singapore news service, Alan Soon, said.
Of the remaining nine sites, seven are run by Singapore Press Holdings, whose publications tend to maintain a pro-government stance. The other two are operated by state-owned broadcaster Mediacorp.
Conditions for the sites that require individual licenses, which have to be reviewed annually, include a performance bond of S$50,000 ($39,700) and a requirement that objectionable content be removed within 24 hours when directed by the MDA.
The MDA said the new regulation did not apply to blogs, though adding: "If they take on the nature of news sites, we will take a closer look and evaluate them accordingly".
The regulation drew criticism from some internet users who saw it as an attempt to stifle online news not affiliated with the government.
On state-owned Channel NewsAsia's Facebook page, a person named Jeremy Tan likened the development to what goes on in China or North Korea.
"You can try to shut us up. We will find a way around it," another internet user, Sushikin Ky, said on the Facebook page.
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