As Internet service providers, telcos Singtel and StarHub said they do not have the tools to monitor and selectively block the content of third-party materials sent through their networks.
For this reason, they are unable to adequately tackle deliberate online falsehoods on their own, both telcos told the parliamentary Select Committee on fake news yesterday.
Measures they have taken, like blocking a website, are also "blunt instruments" that cannot specifically target the root of the problem.
These limitations were highlighted in their oral and written representations to the committee.
But they agreed that a multi-pronged approach should be taken in addressing the issue, including public education and legislation.
Explaining its limitations, Star-Hub's head of regulatory affairs, Mr Tim Goodchild, said that while it can, say, block customers' access to a single domain like Twitter or Facebook, it will not be able to restrict access to individual tweets or posts.
It is also possible for users to circumvent such measures, he added.
The situation is further complicated by the speed at which such posts can travel and become viral, he said when replying to Senior Minister of State for Communications and Information Janil Puthucheary, a committee member.
Mr Sean Slattery, Singtel's vice-president in charge of regulatory and interconnect matters, agreed.
He also said the role of public telecommunications licensees, like his company, is not to play "judge and jury" of content, especially in the light of the heightened privacy and security laws and push to encrypt content.
In fact, the Telecommunications Act prohibits such a licensee from familiarising itself with the content of a message.
But both telcos agreed fake news is a pressing issue. Singtel itself has been a victim of commercial scams out to obtain personal information or money. "There is very little recourse for us," said Mr Slattery.
Public education is just one element of the solution, both representatives told Dr Janil.
Unlike tech giants such as Facebook and Twitter, both telcos said extra legislation may be needed to effectively fight deliberate online falsehoods.
"They are platforms that reach billions of people. If they want to be socially responsible, they do have an obligation to contain the spread of deliberate online falsehoods," said Mr Yuen Kuan Moon, Singtel's chief executive of Singapore consumer business.