Four people have been arrested in a Syria-related counter-terrorism investigation.
Two men from Sheffield, aged 40 and 36, were held this morning on suspicion of an offence under Section 5 of the Terrorism Act, which covers preparation to commit an act of terrorism.
In addition, a 55-year-old woman and a 44-year-old man from Batley, West Yorkshire, were arrested over suspected terrorist fundraising.
Separately, Scotland Yard said a 23-year-old man was arrested in east London today on suspicion of "the commission, preparation or instigation of terrorism".
The arrests in Yorkshire were made by officers from the North East Counter Terrorism Unit, which said in a statement: "Two men from Sheffield aged 40 and 36 have been arrested on suspicion of an offence under Section 5 of the Terrorism Act - preparation to commit an act of terrorism.
"A 55-year-old woman and a 44-year-old man from Batley have been arrested on suspicion of an offence under Section 15 of the Terrorism Act - terrorist fundraising.
The unit added: "The investigation is Syria-related."
The four suspects have been taken to a police station in West Yorkshire for questioning, while five properties in Sheffield, Batley and Dewsbury are being searched.
Detective Chief Superintendent Clive Wain said: "We understand that people may be concerned following today's arrests, however we would like to reassure communities that today's activity is as a result of an ongoing investigation which is intelligence led.
"There is no evidence to suggest that communities are at risk."
Meanwhile, officers from the Met Police's Counter Terrorism Command attended a residential arrest in east London and detained a 23-year-old man.
He was arrested under section 41 of the Terrorism Act 2000 on suspicion of the commission, preparation or instigation of terrorism.
A spokesman said: "Officers continue to search the address and a second residential address in east London. The man is being detained under Schedule 8 of Terrorism Act 2000 legislation.