The trio were not directly named by Australian Security Intelligence Organisation director-general Mike Burgess in the 2025 Lowy Lecture on Tuesday night.
But identifying them may not have been necessary.
"The countries that I didn't mention by name know who I'm talking about," he said in conversation with Lowy Institute executive director Michael Fullilove.
"We know who they are.
"By mentioning them publicly I'm also putting them on notice that we know some of you are prepared to do this and we will do our damnedest to stop it before it happens."
During his speech, Mr Burgess said the degrading trajectory of Australia's security environment alongside regimes' growing willingness to do harm had formed the foundation of ASIO's assessment.
"There is a realistic possibility a foreign government will attempt to assassinate a perceived dissident in Australia," he said.
"We believe there are at least three nations willing and capable of conducting lethal targeting here.
"This threat is real."
Some could try to hide their involvement by hiring criminal cut-outs, Mr Burgess said, pointing to a similar tactic used by Iran when it ordered the 2024 firebombings at Melbourne's Addas Synagogue and Sydney's Lewis Continental Kitchen.
He also mentioned recently uncovered links between between pro-Russia influencers in Australia and an offshore media organisation that "almost certainly" receives orders from Russian intelligence.
Another incident included a foreign intelligence service attempting to recruit Australians to gather information on the economy, critical minerals and the country's nuclear submarine agreement with the US and UK.
Though Mr Burgess's address did not name China, the spy chief was asked about the country's absence.
"I did not mention China in my remarks today," he said.
"But how do you know I wasn't talking about things China did, in my remarks today?"
He chose not to name China primarily because his address was about factors that fray Australia's social fabric.
"At the extreme end of that, that isn't China," he said.
"Although we do have some concerns there too."
The internet's ability to incubate disaffection, international conflicts like the war in the Gaza Strip, and extremist groups such as the National Socialist Network were all said to have played a role in the country's deteriorating social cohesion.
