The UK government is to establish a new unit to counter "fake news", Downing Street has said.
Theresa May's spokesman said the "dedicated national security communications unit" would be charged with "combating disinformation by state actors and others".
"We are living in an era of fake news and competing narratives," he said.
The phrase "fake news" has recently emerged and is frequently used by US President Donald Trump.
What is fake news?
Completely false information, photos or videos purposefully created and spread to confuse or misinform
Information, photos or videos manipulated to deceive - or old photographs shared as new
Satire or parody which means no harm but can fool people
A committee of MPs is currently carrying out an inquiry into the "growing phenomenon" and has demanded information from Facebook and Twitter including on Russian activity during the EU referendum.
Downing Street told political reporters: "The government will respond with more and better use of national security communications to tackle these interconnected complex challenges.
"We will build on existing capabilities by creating a dedicated national security communications unit. This will be tasked with combating disinformation by state actors and others. It will more systematically deter our adversaries and help us deliver on national security priorities."
Last month the BBC launched a new scheme to help young people identify real news and filter out fake or false information.
The new fake news unit was agreed at a meeting of the National Security Council (NSC).
The NSC had also commissioned a defence spending review "to deliver better military capability and value for money in a sustainable and affordable way", Downing Street said.
There have been repeated warnings about cuts to the armed forces, with the Ministry of Defence looking for savings of £2bn.
The latest review, called the Modernising Defence Programme, will be led by the MoD, rather than the NSC, which BBC defence correspondent Jonathan Beale described as a "small but significant victory" for Defence Secretary Gavin Williamson.
The NSC had been carrying out a "capabilities review" expected to push through more defence cuts, our correspondent said.
And handing responsibility to the MoD would give it the chance to argue for more money from the Treasury and more control over the process.