MANCHESTER, England (AP) " The Latest on the blast at an Ariana Grande concert in northern England (all times local):

7:10 a.m.

Greater Manchester Police have raised the death toll in a blast at an Ariana Grande concert to 22.

The force's chief constable, Ian Hopkins, said Tuesday they believe one person carried out the attack. Police are trying to determine if the person acted alone or had support in the Monday night blast.

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Police say some 400 officers were deployed overnight to help with the investigation.

Officials say children are among the victims.

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7 a.m.

Police say they are treating an explosion at an Ariana Grande concert in northern England as terrorism. Greater Manchester Police says the blast killed at least 19 people, and the ambulance service says 59 people have been taken to hospitals.

Greater Manchester Police Chief Constable Ian Hopkins says police are treating the blast as an act of terrorism "until we know otherwise."

There was panic after the explosion, which struck around 10:30 p.m. (2130 GMT) Monday night as Grande was ending the concert.

Grande, who was not injured, tweeted hours later: "Broken. From the bottom of my heart, I am so so sorry. I don't have words."