British counterterrorism police were investigating two suspected improvised explosive devices discovered in an unoccupied flat in northwest London on Wednesday.
The block of flats in Harlesden was evacuated during the operation to make the devices safe and residents have since been allowed to return, London's Metropolitan Police said in a statement.
The devices are undergoing forensic examination and the force's Counter Terrorism Command has launched an investigation.
Chief Superintendent Simon Rose called on the public to come forward with any information.
"I also want to reassure the local community that we have carried out precautionary searches in the surrounding area to make sure there was nothing else of a similar nature nearby, which I'm pleased to confirm is the case," he said.
Britain is on its second-highest threat level after several attacks in 2017.