Iran was behind at least 20 deadly plots in the UK over the past two years, according to the head of MI5, as he warned of an increased terror risk linked to the conflict in the Middle East.
In a speech at the Counter Terrorism Operations Centre in West London, Ken McCallum said that Isis and Al Qaeda were on the rise again and attempting to "export terrorism."
He told his audience: "Al Qaeda had sought to capitalise on conflict in the Middle East, calling for violent action."
Isis was of particular concern, the MI5 Director General said.
"Today's Islamic State is not the force it was a decade ago. But after a few years of being pinned well back, they've resumed efforts to export terrorism.
"The ISKP (Islamic State Khorasan Province) attack in Moscow was a brutal demonstration of its capability."
Ken McCallum said that ISIS and Al Qaeda were on the rise again and attempting to 'export terrorism'Ken McCallum said that ISIS and Al Qaeda were on the rise again and attempting to 'export terrorism'The attack on a Moscow concert hall last March was the worst terror atrocity in Russia in recent years, killing 145 people and injuring 500 others.
Ken McCallum said: "We and many European partners are detecting IS-connected activity in our homelands, which we are moving early to disrupt."
To illustrate the increasing threat, he revealed that over the last month, more than a third of MI5's top priority investigations have had some form of connection to organised overseas terrorist groups.
"Late last year, a man in Coventry was jailed for life for designing a 3D-printed armed drone for IS in west Africa," he said.
"Just a few weeks earlier, two brothers from Birmingham were jailed for an attempt to join ISKP in Afghanistan.
"These cases are not wild outliers. More will be coming through the courts. Organised groups have the numbers and the know-how to carry out, or inspire, horrendous mass causality attacks."
MI5 chief said that roughly 75 per cent of terror threats his teams were dealing were Islamist inspired, and 25 per cent were related to far-right extremism.
He revealed that police and MI5 had foiled 43 late-stage terror plots since 2017, with some of those plotters attempting to get hold of firearms and explosives.
Ken McCallum said the attack on a Moscow concert hall was an example of the resumed efforts of Isis and Al Qaeda
The evolving conflict between Israel and Iran and its terror proxies, pose a heightened risk at home, he warned.
"We are powerfully alive to the risk that events in the Middle East directly trigger terrorist action in the UK, as we saw with last October's knife attack in Hartlepool.
"The ripples from conflict in that region will not necessarily arrive at our shores in a straightforward fashion; they will be filtered through the lens of online media and mixed with existing views and grievances in unpredictable ways."
The MI5 Director General said that State actors like Iran also pose a growing threat, and could be triggered into further aggression by war in the Middle East.
"Since January 2022, with police partners, we have responded to twenty Iran-backed plots presenting potentially lethal threats toBritish citizens and UK residents.
"As events unfold in the Middle-East, we will give our fullest attention to the risk of an increase in, or broadening of Iranian state aggression in the UK.
"Like the Russian services, Iranian state actors make extensive use of criminals as proxies.
"Last December, a man was jailed for reconnaissance he had carried out against the then-headquarters of the Iran International media organisation."
MI5 is also seeing an increase in the number of people attempting to travel abroad to join up with terror groups.
Although not on the same scale as the exodus to join up with ISIS almost a decade ago, Mr McCallum said: "We are seeing a bit of an upswing in attempts to travel overseas".
More broadly, the threat from state actors has seen a dramatic rise in recent months.
Over the past year, the number of state threat investigations being run by MI5 has increased by 48%. Russia in particular, is posing an increasing threat to the UK, the MI5 boss said.
"The UK's leading role in supporting Ukraine means we loom large in the fevered imagination of Putin's regime, and we should expect to see continued acts of aggression here at home.
The GRU (Russian military intelligence) .. is on a substantial mission to generate mayhem on British and European streets. We've seen arson, sabotage and more. Dangerous actions conducted with increasing recklessness."