A potential network of terror plotters behind the Parsons Green bombing is being hunted by police as the country braced for a further attack.
The country's top counter-terrorism officer suggested on Friday night that more than one suspect could have been involved in the attempt to slaughter commuters in a tube carriage.
Assistant Commissioner Mark Rowley said police were "chasing down suspects", while suggestions were made by Donald Trump that the bomber was known to Scotland Yard.
Security Minister Ben Wallace told the BBC on Saturday: "We haven't been able at the moment to catch the bomber. The bomber is still out there - or bombers - and we have to get to the bottom of that and follow up the leads."
The improvised device - reportedly containing the explosive triacetone triperoxide (TATP) and packed with nails - was dumped on a busy District Line train during Friday rush hour.
Its detonation from inside a bucket, which is thought to have only been partial, injured 29 people.
Parsons Green station was re-opened in the early hours of Saturday, shortly after the Prime Minister announced the Joint Terrorism Analysis Centre set the terror threat at its highest level.
It was the second time this year the country was placed at "critical", meaning an attack "may be imminent", the Prime Minister said - the other occasion being the Manchester Arena bombing which killed 22 people in May.
Mr Wallace suggested CCTV images of the bomber could be released as part of the manhunt for those responsible, but Scotland Yard subsequently denied there were any plans to do so.
S7 trains such as the one involved in Friday's incident have video cameras installed inside all seven carriages and there are more than 12,000 cameras across London Underground's stations and trains.
Asked on the BBC Radio 4 Today programme if it was surprising that no CCTV had yet been released, he said: "I totally agree that CCTV footage is useful and no doubt at some stage that will come but the conduct of the investigation I leave to the police and the security services."
It came after Scotland Yard and the Prime Minister rebuked the US president over his claim the Parsons Green Tube bomber was "in the sights" of detectives.
A total of 21 patients remain in hospital following the blast, according to the latest NHS England figures, with another eight discharged. Most had suffered "flash burns", police said.
There were fears the number of those hurt could have been much higher - with the real potential for life-threatening injuries - had the bomb, which was concealed within a supermarket carrier bag, fully detonated.
It is not yet known whether the bomb, which was reportedly fixed with a timer, went off at its intended target. The train - bound for Edgware Road - was just pulling into the District Line station in south-west London when the device exploded, in the rear carriage, sending rush-hour passengers fleeing to safety.