Many at the concert were young girls and teens enthralled by Grande's pop power.
She said 3,800 soldiers will be deployed across Britain to step up security amid fears of a wider plot.
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.
The police arrested three men in Manchester on Wednesday as part of their investigation, bringing to four the number of people who have been taken into custody so far.
Forensic officers work near the Manchester Arena in Manchester, Wednesday, May 24, 2017.More news: Clemens' 2 home runs lift Texas past Oklahoma 8-4
"I have been very clear with our friends that should not happen again", Rudd said.
The pictures were apparently taken by police investigators and, according to British government ministry sources, leaked by U.S. counterparts they had been shared with.
The 23-year-old singer - who performed in Dublin last weekend, and was not injured in the Manchester attack - had been scheduled to perform in London this week, before moving on to Europe.
The United Kingdom's domestic security service escalated the national terror threat level Tuesday from severe to critical.
Abedi is confirmed to have attended Burnage Academy for Boys secondary school and, briefly, the University of Salford, both in Manchester. Neighbors recalled him as a tall, thin young man who often wore traditional Islamic dress and did not talk much.
It said security services were concerned further bombs could have been created by a network intent on carrying out further attacks.More news: Trump urges grads to draw lessons from his outsider status
Officials are probing how often Abedi had traveled to Libya, which has seen an eruption of armed Islamist groups since dictator Moammar Gadhafi was overthrown and killed in 2011.
French Interior Minister Gerard Collomb said British investigators had told French authorities Abedi had probably travelled to Syria as well. ISIS issued a claim of responsibility Tuesday, but the level of the terrorist group's involvement isn't known.
But a former Libyan security official alleged that Ramadan Abedi was himself member of a former al-Qaida-backed group in Libya. Twenty of those with traumatic injuries are still in critical condition.
Many of those still hospitalised had serious wounds that will require "very long term care and support in terms of their recovery", Rouse said.
Officials said all those hospitalised had been identified.
"What is more of a danger is division and communities turning against each other".
"But the overall impression I've had here is of a city doing its absolute best at a time of agony and grief to pull together".More news: Canadian connection: Drake meets Celine Dion at Billboards
"They deserve it", she said. "It was a lot of children with blood all over them - crying and screaming".