Police are questioning three men held under the Terrorism Act following a raid at a house.
Two 24-year-olds and a 41-year-old were initially arrested on suspicion of drug offences by Gwent Police at a house in Blackwood, South Wales, on Wednesday.
Following further inquiries, the Metropolitan Police Service Counter Terrorism Command was called in the following day and further arrested the trio on suspicion of the commission, preparation or instigation of acts of terrorism under the Terrorism Act 2000.
They were subsequently transferred from South Wales to a police station in the central London area.
A spokeswoman for Gwent Police said the inquiry was not linked to international terrorism.
A resident from the street, who asked not be named, said a bomb disposal team had arrived in the vicinity. She added: "I don't suppose we are in any danger because the police would have cleared us away.
"It did take over 24 hours for them to get here so they can't be in much of a hurry. It can't be a major thing."
Another neighbour, who also wished to remain anonymous, said: "I have got no idea how long the men lived there.
"They were supposed to be builders and it was supposed to be chemicals that were found there.
"There are police officers guarding the front and the back."
