Detectives are probing a possible terror "network" linked to the Manchester suicide bomber, as six people are arrested in connection with the attack.
Police had earlier named British-born Salman Abedi, 22, as the perpetrator of the bombing at the Manchester Arena indoor venue at the end of a concert by US pop singer Ariana Grande on Monday, attended by thousands of children and teenagers.
"A strong, capable and united North Atlantic Treaty Organisation is at the heart of the security of each and every one of our nations", she is expected to say, according to a senior government official.
Abedi also said he was certain Salman had not been in Syria.
On Wednesday morning, Manchester police arrested three men in the south of the city in connection with the bombing, taking the total number of suspects in custody in the United Kingdom to four. Armed police were also seen on patrol outside St. Paul's Cathedral in London, another popular tourist spot. The defense ministry said the changing of the guard ceremony at Buckingham Palace has been cancelled so that police officers can be redeployed elsewhere.
United Kingdom police make 7th arrest in Manchester terror probe
ISIS has issued a claim of responsibility for the bombing, but the level of the terrorist group's involvement isn't known. Including an arrest that was announced Tuesday, police have now said they've made five arrests related to the attack.
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.
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 once attended Salford University there.
Police have found more explosives that could have been used in further attacks, the Independent reported, citing security services. Neighbors recalled him as tall, thin and quiet, and said he often wore traditional Islamic dress.
Meanwhile, Prime Minister Theresa May on Wednesday morning chaired a meeting with her emergency security cabinet, known as Cobra, to collect intelligence reports on the attacker.
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Officers also carried out a search of a property in Whalley Range.
French Interior Minister Gerard Collomb told local broadcaster BFM that the 22-year-old is thought to have also travelled to Syria, adding that he had proven links to the so-called "Islamic State" jihadist group.
"But it worries me greatly and in fact I made known my concerns about it to the USA ambassador", he said, adding: "The British police and security services need to be in the lead when this is a live investigation here". He did not elaborate but said it's unclear whether Abedi was part of a larger network of attackers.
Counter terror police chiefs said the leak undermined their investigation and victims' and witnesses' confidence.
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.
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His 13 playoff points led the Predators offensive threat, and finding someone to fill that void will be clutch for Nashville . Aberg had two points in 15 regular-season games for the Predators, and has two points (1 G, 1 A) in nine playoff contests.
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