UK on highest terror alert, deploys army

British security forces arrested three more suspects on Wednesday in connection with the Manchester concert bombing and sent hundreds of soldiers 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 on Monday night in Manchester. She said he had been known to security forces "up to a point".
"I think it's very clear that this is a network that we are investigating," police chief Ian Hopkins told reporters outside Manchester police headquarters.
Officials are examining Abedi's trips to Libya and possibly Syria as they piece together his allegiances and try to foil any new potential threats. The government said nearly 1,000 soldiers were deployed on Wednesday instead of police in high-profile sites in London and other locations.
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.
The changing of the guard ceremony at Buckingham Palace was cancelled on Wednesday so police officers can be re-deployed, Britain's defense ministry said.
The Palace of Westminster, which houses the British Parliament, was also closed Wednesday to all those without passes, and tours and events there were cancelled until further notice.