London police have confirmed a second arrest has been made following the London underground attack.
A 21-year-old man was arrested in Hounslow late on Saturday night, UK time.
He was arrested under section 41 of the Terrorism Act.
It follows a previous arrest made over the incident, where an 18-year-old Dover man was taken into custody.
30 people have been killed after the bomb went off at Parsons Green station, but no one was killed.
Senior national co-ordinator for counter terrorism policing Neil Basu earlier thanked the public and expressed his thoughts for the injured.
"In total, we know that 30 people have received treatment at hospital for injuries. We are incredibly grateful that no one was killed yesterday but my thoughts are with those people and everyone affected by this terrible and traumatic attack," he said in a statement.
"I would like to finish by thanking the public for their support at this crucial time.
"The fact that so many communities stand together against the cowardice that is terrorism is a tremendous strength here in the UK."