British police have made a second arrest in relation to Friday’s bombing of a London train carriage.
A 21-year-old man was arrested in Hounslow before midnight Saturday night local time, the London Metropolitan Police Counter Terrorism Command in a statement.
It follows the arrest of an 18-year-old man in Kent suspected in relation to bombing that injured 29 people on a London train on Friday, which police described as "significant".
Authorities investigate the scene in southwest London. Source: AAP
"We have made a significant arrest in our investigation this morning," Neil Basu, Senior National Co-ordinator for Counter Terrorism Policing, said in a statement.
"Although we are pleased with the progress made, this investigation continues and the threat level remains at critical."
Both men were arrested under section 41 of the Terrorism Act.
It's believed the explosion may have been triggered by the contents of this bag. Source: Twitter/ Johnny50
British police said earlier they were keeping an open mind on whether more than one person was responsible for the bombing.
"We are still pursuing numerous lines of enquiry, and at great pace," Mr Basu told reporters.
"Our priorities are ... to identify and locate any other potential suspects."