Swedish Foreign Minister Carl Bildt has said the British-educated Stockholm suicide bomber missed causing large numbers of casualties in Saturday's incident by a matter of minutes.
Mr Bildt said 28-year-old Taimour Abdulwahab al-Abdaly was heading towards crowds of Christmas shoppers when explosives he was carrying apparently went off prematurely.
The Swedish authorities are working closely with their UK counterparts to investigate the attack, in which al-Abdaly was killed and two other people injured.
The Iraq-born graduate of Bedfordshire University left his wife and three children at their family home in Luton to travel to Sweden several weeks ago.
In a BBC television interview last night, Mr Bildt said investigators were making an 'intensive' effort to work out if al-Abdaly was acting alone or with accomplices.
Mr Bildt also said Swedish media were reporting that al-Abdaly 'was profoundly transformed by something that happened while he was in the UK'.
But asked if he believed the bomber was radicalised in Britain, he replied: 'We don't know and it might be that we never find out.'
Mr Bildt said: 'It looks like he was heading into probably the most crowded place in Stockholm at the most crowded time of the year.
'He was heading into a place where, if he had exploded all the ordnance he had with him - and that was quite substantial - it would have been mass casualties of a sort we haven't seen in Europe for quite some time.
'(We were) just minutes and a couple of hundreds of metres away from something catastrophic.'
Al-Abdaly was driven out of Luton Islamic Centre for preaching about suicide bombings and attempting to recruit extremists, according to religious leaders.
Asked whether he was disappointed that the Luton mosque's concerns about al-Abdaly's radicalism were not passed on to security services, Mr Bildt said: 'To express radical opinions is one thing. There are a number of people who have radical opinions.
'We live in societies where we very much value freedom of opinion and freedom of speech.
'But whether there was something there that should have been picked up or not, I think we have to leave that for somewhat later.'
