英国官员：情报部门知悉曼彻斯特爆炸案嫌疑人的情况

British police say they have arrested three more people in connection with the investigation into Monday's deadly bombing after a concert in Manchester.

A statement Wednesday from Greater Manchester Police said only that the arrests came after officers executed warrants in South Manchester. There was no information about how the three men, or a fourth man arrested Tuesday who was only identified as a 23-year-old, might be involved in the attack.

British interior minister Amber Rudd said Wednesday the suicide bomber, who has been identified as 22-year-old Salman Abedi, was "known" by British intelligence services before the bombing. She also told the BBC that "it seems likely, possible, that he wasn't doing this on his own."

Investigators have been working since Monday's attack to determine if the bomber was part of a wider group.

Mark Rowley, who heads the National Counter Terrorism Policing, described the investigation late Tuesday as "making good progress" and following a number of leads. But he said authorities cannot yet say if the Abedi acted alone.

His comments came after a panel that sets the country's terrorism alert level raised it to critical, or the highest step, signaling that another attack was highly likely and could be imminent.

The change is most visible in the deployment of soldiers to help guard certain areas, including major events such as concerts and football matches, in order to free up police officers.

The blast at the conclusion of a concert by American pop star Ariana Grande at Manchester Arena killed 22 people and wounded 59 others. The attacker also died at the site.

Islamic State is claiming it was behind the attack, but neither British nor U.S. intelligence have confirmed that.