It was the deadliest attack in Britain since July 2005, when four British Muslim suicide bombers killed 52 people in coordinated attacks on London's transport network.
Three more people have been arrested by police investigating the attack on an Ariana Grande concert in Manchester, U.K. this week.
Foreign Minister Ri Yong-Ho sent a similar message to his British counterpart Boris Johnson. Police confirmed that 22 people were killed in an explosion following a Ariana Grande concert at the venue late Monday evening.
North Korea has generally frosty relations with Western nations, which are seeking tougher sanctions meant to curb its missile and nuclear programmes.
Suicide bomber Abedi was born in Britain to a Libyan family, grew up in Manchester's southern suburbs and attended local Salford University for a time.
Military personnel and police have been deployed to protect key sites including Buckingham Palace, Downing Street, the Palace of Westminster and embassies.
"So until we can be reassured that there is no continued activity around this operation, that it is entirely safe around this operation, then it is right that we are at this heightened state of alert".
The terror threat level was increased after investigations revealed Abedi may not have acted alone.More news: Philippine President Rodrigo Duterte declares martial law
In March, a British-born convert to Islam plowed a vehicle into pedestrians on London's Westminster Bridge, killing four people, before stabbing to death a police officer who was on the grounds of parliament.
"We stand defiant", she said.
Britain's Prime Minister Theresa May raisedi the country's terror threat level from "severe" to "critical" Tuesday after law enforcement raided the home of the Abedi. A man reported to be Abedi's brother had been arrested on Tuesday.
Manchester police arrested a man early Wednesday at a house just a 10-minute walk from Abedi's home.
Islamic State, now being driven from territories in Syria and Iraq by Western-backed armed forces, claimed responsibility for the Manchester attack, but there were contradictions in its accounts of the action and a telling lack of detail.
Runshaw College in Leyland, Lancashire said Callander expressed "enormous sadness" at her death, saying she was on the second year of her health and social care course.
Chris Upton, the head teacher at the Tarleton Community Primary School, described her as "simply a lovely little girl" who was "quiet and unassuming with a creative flair".
Rudd also scolded US officials for leaking details about the investigation into the Manchester attack before British authorities were prepared to go public.
Ismail was arrested by armed police in Chorlton, south Manchester. Officials say 20 of them are being treated for critical injuries. Oliver also confirmed that another Year 9 student, Freya Lewis, was badly injured in the attack.