A second man has reportedly been arrested in London over an Islamic State attack on a rush-hour train in London on Friday.
UK police made the arrest late Sunday afternoon AEST in relation to the explosion on the packed train that injured at least 29 people.
The 21-year-old is said to have been arrested in Hounslow in London's west.
The second arrest comes after an 18-year-old British man was detained by police on Saturday in connection to the attack.
The teen was arrested on Saturday in Dover, South East England, under section 41 of the UK's Terrorism Act and is expected to be transferred to a south London police station.
The commuters were injured after the improvised bomb detonated on the packed train at Parsons Green. The explosion is the fifth terrorist attack in Britain this year.
Metropolitan Police Deputy Assistant Commissioner Neil Basu said that investigations were continuing despite the "significant arrest".
"The public should remain vigilant as our staff, officers and partners continue to work through this complex investigation. We are not, at this time, changing our protective security measures and the steps taken to free up extra armed officers remain in place," he said in a statement.
The UK terror threat level was raised from severe to critical on Friday evening local time following the explosion.
Prime Minister Theresa May said that "military personnel would replace police officers on guard duties at certain protected sites that are not accessible to the public."
More to come.