An Iraqi teenager on Friday pleaded not guilty to allegations he was behind the attempted bombing of a London underground train last year which left 30 people injured.

Ahmed Hassan, 18, is facing charges of attempted murder and causing an explosion over the September 15 attack at Parsons Green station.

Wearing a purple jumper, Hassan appeared at the London court by video link from prison.

The blast, which occurred during rush hour, inflicted flash burns on passengers, while others were injured in the subsequent panic to escape the packed London Underground train.

Thirty people were treated in hospital following the explosion, which could have had a far more devastating impact but failed to detonate correctly.

The device had been placed in a plastic bag and contained hundreds of grams of explosives, as well as metal shrapnel including knives and screws, a prosecutor said during an earlier court hearing.

The bombing at Parsons Green, a quiet and wealthy neighbourhood, was Britain's fifth terror attack in six months and was claimed by the Islamic State group.

Hassan was arrested a day after the bombing when he was recognised by an officer at the southeastern ferry port of Dover.

He had been living in Surrey just south of London and has said his parents were killed in Iraq.

The two-week trial is due to start on March 5, after a further hearing scheduled for February 23.