If confirmed as a terrorism incident, it would be the deadliest attack in Britain by militants since four British Muslims killed 52 people in suicide bombings on London's transport system in July 2005.
At least 19 people were killed in a blast at a concert in the English city of Manchester on Monday where singer Ariana Grande had been performing and two USA officials said a suicide bomber was suspected in the explosion.
"We're dealing with injuries to major organs, we're dealing with loss of limbs potentially, we're dealing with embedded objects, all the horrific injuries that you would expect from the event that happened", said Jon Rouse, chief officer of the Greater Manchester Health and Social Care Partnership, who added that the victims were receiving "round-the-clock" treatment.
Foreign Minister Ri Yong-Ho sent a similar message to his British counterpart Boris Johnson.
Among the dead is 8-year-old Saffie Roussos and 18-year-old Georgina Collander, who took a picture with Grande two years ago.
North Korea has generally frosty relations with Western nations, which are seeking tougher sanctions meant to curb its missile and nuclear programmes.
"It is with enormous sadness that it appears that one of the people who lost their lives in Monday's Manchester attack was one of our students here at Runshaw College", the school said in a statement.
Tottington High School in the town of Bury said the school community was "absolutely devastated and heartbroken" at the news Wednesday that Olivia was killed in the blast.
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Soldiers were seen at the Houses of Parliament, Prime Minister Theresa May's Downing Street residence and at London police headquarters at New Scotland Yard.
In the wake of the attack the U.K.'s terrorist threat level has increased to "critical" for the first time since 2007. But police say they're still working to determine whether Abedi had help in planning the bombing.
Abedi was first revealed as the attacker on Tuesday by CBS in the USA, prompting United Kingdom police to put out a statement saying speculation was "unhelpful and potentially damaging" to the investigation.
"She was loved by everyone and her warmth and kindness will be remembered fondly", Upton said.
The Islamic State terror group claimed responsibility for the barbaric attack, which involved a home-made device packed with nuts and bolts which exploded in the venue's foyer as thousands of young people were leaving. He declined to give any further details on the investigation.
The Metropolitan police has confirmed that there would be more stop and search and vehicle checkpoints with nearly 1,000 British soldiers being deployed on streets from Wednesday. Oliver also confirmed that another Year 9 student, Freya Lewis, was badly injured in the attack.