The so-called Islamic State (IS) group would be prepared to carry out a chemical weapons attack on the UK, security minister Ben Wallace has said.
While no specific plot has been identified, IS has “aspirations” for mass casualty attacks, he said.
In a Sunday Times interview Mr Wallace said there have been reports of IS using poisonous gas in Iraq and Syria.
“They have no moral objection to using chemical weapons… and if they could, they would in this country,” he said.
He also pointed to a recent Europol report, which said there was evidence that IS has shown an interest in the use of chemical or biological weapons, and the potential realisation of “everybody’s worst fear” in Europe.
Mr Wallace told the Sunday Times: “The ambition of IS or Daesh is definitely mass casualty attacks.
“They want to harm as many people as possible and terrorise as many people as possible.”
He said that Moroccan authorities raided an IS cell in February which had substances that could have been used to either make a bomb or a “deadly toxin”.
Mr Wallace also warned of the “enemy within” – with terror groups, Russia and cyber attackers trying to plant “traitors” in the government, the military and leading businesses.
He said: “The insider threat, as we would call it, is real and it can be exploited and there are people trying to do that as we speak.
“If it’s hard to get in the front door, then what you try and do is get someone on the inside.”
Last month, the head of MI6 said the scale of the terrorism threat to the UK is “unprecedented”.
Alex Younger said UK intelligence and security services had disrupted 12 terrorist plots since June 2013.
He said many of the threats came from ungoverned spaces in the Middle East – namely Iraq and Syria.
Mr Younger also warned that “hybrid warfare”, which included cyber-attacks and subverting democracy, was becoming an “increasingly dangerous phenomenon”.
The threat level for international terrorism in the UK has been severe – meaning an attack is highly likely – since August 2014.
There are five threat levels – low, moderate, substantial, severe and critical – set by MI5’s Joint Terrorism Analysis Centre.