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. She said he had been known to security forces "up to a point."
Officials are examining Abedi's trips to Libya as they piece together his allegiances and try to foil any new potential threats.
Police said three men were arrested 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 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. The traditional ceremony is a major tourist attraction in London.
The Palace of Westminster, which houses the British Parliament in London, was also closed Wednesday to all those without passes, and tours and events there were cancelled until further notice. Armed police were also seen on patrol outside St. Paul's Cathedral in London, another popular tourist spot.
Officials said 984 soldiers were deployed Wednesday in London and in other locations.
Suicide bomber Abedi was born in Britain to a Libyan family, grew up in Manchester's southern suburbs and attended local Salford University for a time.
Police on Tuesday raided his house, using a controlled explosion to blast down the door. Neighbors recalled him as a tall, thin young man who often wore traditional Islamic dress and did not talk much.
British Prime Minister Theresa May chaired a meeting Wednesday of her emergency security cabinet group to talk about intelligence reports on Abedi and concerns that he might have had outside support.
Police also raided and searched a property elsewhere in Manchester where Abedi's brother Ismail is thought to have lived.
Officials are probing how often Abedi had traveled to Libya, which has seen an eruption of armed Islamist groups since dictator Moammar Gadhafi was overthrown and killed in 2011.
France's interior minister said Abedi is believed to have traveled to Syria and had "proven" links with the Islamic State group.
Minister Gerard Collomb said Wednesday on BFM television that British and French intelligence have information that Abedi had been to Syria. He did not elaborate but said it's unclear whether Abedi was part of a larger network of attackers.
British officials have not commented on whether Abedi had links to IS or other extremist groups.
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.
She also complained about U.S. officials leaking sensitive information about Abedi to the press. Rudd said Britain's operational security could be harmed by the leaks, taking "the element of surprise" away from security services and police.
"I have been very clear with our friends that that should not happen again," she said.
In addition to those killed in the concert attack, Manchester officials raised to 119 the number of people who sought medical treatment after the attack, including those who traveled to hospitals on their own.
Sixty-four people are still hospitalized, Jon Rouse of the Greater Manchester Health and Social Care Partnership said Wednesday. Officials say 20 of them are being treated for critical injuries.
Many of those still hospitalized had serious wounds that will require "very long term care and support in terms of their recovery," Rouse said.
Officials said all those hospitalized had been identified.
Soldiers were replacing armed police on Wednesday at sites like Buckingham Palace, 10 Downing Street and Parliament. London Police Commander Jane Connors said the goal is to "make our city as hostile an environment as possible for terrorists to plan and operate."
She said armed police patrols had been increased and will be ready to respond quickly to any incidents.
Collomb, who spoke with May after the attack, said the two countries should continue cooperating closely on counterterrorism efforts despite Britain's pending exit from the 28-nation European Union.