The United States is planting "digital bombs" in Russia's infrastructure in response to the alleged hacking of last year's presidential election, it has been claimed.
Former President Barack Obama authorised the "implants" of cyber weapons in the final weeks of his Administration and gave US intelligence agencies power to deploy them in retaliation against any future Russian cyber attack, the Washington Post reported.
The covert programme was described as "the digital equivalent of bombs that could be detonated if the US found itself in an escalating exchange with Moscow".
It also emerged that Obama had received a top-secret memo in August, couriered directly to him by the CIA, detailing Russian President Vladimir Putin's direct involvement in cyber efforts to disrupt the election.
The memo contained details of instructions Putin gave to ensure the defeat of Democratic nominee Hillary Clinton, the Post reported.
Weeks earlier the publication by WikiLeaks of emails hacked from the Democratic National Committee proved damaging to Clinton's campaign.
Obama and his Administration looked at various responses before the election including a retaliatory cyber strike, publishing intelligence about Putin, or crippling economic sanctions. But Obama was concerned he might be perceived as attempting to influence the election in favour of Clinton.
One Obama Administration official told the Post: "I feel like we sort of choked. It is the hardest thing about my entire time in government to defend."
The digital bombs programme involves the NSA, CIA and US Cyber Command and was reportedly a long-term operation with the process of setting it up still under way.
A US official told the Post that the "implants" were being put in computer networks that were "important to the adversary and that would cause them pain and discomfort if they were disrupted".
Agencies would be able to trigger them without Trump's authorisation.
In a statement, Obama's spokesman said his response to the Russian meddling had been "robust ... as is evident by [him] raising this issue directly with President Putin".