Two men have been arrested under the Terrorism Act after police found two 25-litre containers labelled "hydrogen peroxide" in a flat in Bristol.
Two men arrested under the Terrorism Act have been freed without charge after a suspicious substance was identified as "non-hazardous" oil.
The first man was originally arrested on Wednesday on suspicion of drug-related offences, said police.
The men were arrested after police searched a Bristol flat and found two 25-litre containers labelled as holding hydrogen peroxide.
Police suspect a link to terrorist activities, and forensic tests are being carried out on the substances.
The discovery had led officers to suspect a link to terrorist activities.
The second man was arrested after further investigations. Police say there was no threat to public safety.
One of the men is from Afghanistan and in his early 20s, while the other is Somali and in his early 50s.
Assistant Chief Constable Steve Mortimore of Avon and Somerset police said: "These containers are marked hydrogen peroxide. I need to find out urgently what is this chemical inside.
The substance in the containers is thought to be vegetable oil.
"It all hinges on what is this chemical. Hydrogen peroxide has been linked to other terrorist incidents in the country."
Officers found the containers at the flat in Stapleton Road, Easton.
The chemical was used in the 7 July bomb attacks in London in 2005.
'Vigilant'
Officers found the containers at the flat in Stapleton Road, Easton, following the first arrest in the Castle Park area of Bristol.
The men are being held at a police station in the Avon and Somerset area.
Officers have confirmed one is from Afghanistan and in his early 20s, while the other is Somali and in his early 50s.
A statement from the Avon and Somerset force said public safety was their "top priority".
"While this incident does not involve a specific threat to anybody, police are undertaking an extensive investigation."
Officers had been speaking to community leaders in the area to provide information and reassurance, it said.
ACC Steve Mortimore added: "Our message to the public for some time now has been that while we don't want people to be unduly afraid, everyone should be aware of the potential risks and be vigilant."
Kayse Mohammed, editor of The Somali Voice in Bristol, said: "We call on all Muslims and Somalis and the public to work with the police."
