British police and intelligence agencies have arrested three more suspects 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.
She said he had been known to security forces "up to a point". Officials are examining Abedi's trips to Libya as they worked to piece together his allegiances and foil any new potential threats.
Police said three men were arrested on Wednesday in south Manchester, where a day earlier a 23-year-old man was also arrested and a number of homes were searched.
Britain raised its threat level from terrorism to "critical" after an emergency government meeting late on 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 cancelled on Wednesday so police officers could be re-deployed, Britain's defence ministry said.
The Palace of Westminster, which houses the British Parliament in London, was also closed on Wednesday to all those without passes, and tours and events there were cancelled until further notice. Armed police were seen on patrol outside St Paul's Cathedral in London, another popular tourist spot.
Abedi was born in Britain to a Libyan family, grew up in Manchester's southern suburbs and attended the local Salford University for a time.
Police on Tuesday raided his house, using a controlled explosion to blast down the door. Neighbours recalled him as a tall, thin young man who often wore traditional Islamic dress and did not talk much.
British Prime Minister Theresa May Wednesday chaired a meeting of her emergency security cabinet group known as Cobra to deal with the intelligence reports about Abedi and concerns that he might have had outside support.
