Metropolitan Police are scouring CCTV footage to track down suspects responsible for bombing an underground train during rush-hour.
It comes after a bomb exploded on the tube at Parsons Green Underground Station yesterday.
No one was killed in the District Line blast, but at least 29 people were injured.
The UK terror threat level has been raised to the highest level following the incident – now set to critical – which means an attack could be imminent.
Parsons Green Underground Station was reopened in the early hours of this morning.
Controversy was sparked yesterday after smartphone users were seen taking selfies as commuters and tube users fled the scene after the explosion.