MANCHESTER, England (AP) — British police and intelligence agencies arrested three more suspects Wednesday in connection with the Manchester suicide bombing and moved quickly to secure key sites across the country, including Buckingham Palace and the British Parliament at Westminster. Home Secretary Amber Rudd said the bomber, identified as British-born Libyan Salman Abedi, "likely" did not act alone when he killed 22 people and wounded dozens at an Ariana Grande concert Monday night in Manchester. Britain raised its threat level from terrorism to "critical" after an emergency government meeting late Tuesday amid concerns that the 22-year-old Abedi may have accomplices who are planning another attack. British soldiers have been deployed in place of police officers to guard high-profile sites such as Buckingham Palace and Parliament. The changing of the guard ceremony at Buckingham Palace was canceled Wednesday so police officers can be re-deployed, Britain's defense ministry said. Rudd said Britain's increased official threat level will remain at "critical" as the investigation proceeds and won't be lowered until security services are convinced there is no active plot in place.