Forensics investigators work at the Manchester Arena in Manchester, Britain May 23, 2017. Reuters/Darren Staples

British Prime Minister Theresa May said Tuesday that police and security staff believe that they know the identity of the attacker who detonated an explosive Monday night at the Manchester Arena in northern England “but at this stage of their investigations, we cannot confirm his name.” In a statement in Downing Street, May said the attack “stands out for its appalling cowardliness,” and condemned the attacker as “warped and twisted.”

The prime minister said it was “now beyond doubt that the people of Manchester and of this country have fallen victim to a callous terrorist attack that targeted defenseless young people.” At least 22 people were killed and more than 50 others injured in the attack, which appears to be the deadliest terrorist incident in Britain since coordinated attacks on the London public transit network in 2005.

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The attack took place after singer Ariana Grande ended her concert, which was attended by nearly 21,000 people. Following the attack, the “Side to Side” singer, who was scheduled to perform Thursday and Friday at the O2 Arena in London before moving on to Belgium, Poland, Germany, Switzerland, and France for other performances, canceled her tour.

President Donald Trump, who is currently in the West Bank city of Bethlehem, also condemned the “evil losers” behind Monday night’s attack.

“I extend my deepest condolences to those so terribly injured in this terrorist attack and to the many killed and the families – so many families of the victims,” he said, adding: “We stand in absolute solidarity with the people of the United Kingdom. ... So many young beautiful, innocent people living and enjoying their lives murdered by evil losers in life."

He concluded saying: “This wicked ideology must be obliterated – and I mean completely obliterated – and the innocent life must be protected. All civilized nations must join together to protect human life and the sacred right our citizens to live in safety and in peace.”

Britain's Prime Minister Theresa May speaks outside 10 Downing Street in London, May 23, 2017. Reuters/Toby Melville

Relatives of many of those who attended the event are trying to find out if their family members were injured in the attack. However, a full list of the names of the victims has not been released so far. Only one victim of Monday's attack has been identified so far as Georgina Callander, who was studying health and social care at Runshaw College in Lancashire.

"We believe at this stage the attack last night was conducted by one man,” Greater Manchester Police Chief Constable Ian Hopkins said at a televised news conference. “We believe the attacker was carrying an improvised explosive device, which he detonated, causing this atrocity.”

Grande, who was unharmed and safe following the attack, expressed her sadness over the attack.

“Broken. From the bottom of my heart, I am so so sorry. I don’t have words,” Grande tweeted. Her management team also issued a statement to Billboard.

“Tonight, our hearts are broken," the statement read. "Words cannot express our sorrow for the victims and families harmed in this senseless attack. We mourn the lives of children and loved ones taken by this cowardly act,” the statement continues. “We are thankful for the selfless service tonight of Manchester's first responders who rushed towards danger to help save lives. We ask all of you to hold the victims, their families, and all those affected in your hearts and prayers,” it added.