Britain's terror threat level was lowered from "critical" to "severe", Prime Minister Theresa May said Saturday after meeting with security leaders.
About 1,000 armed police officers have been freed by a decision to deploy the Army to protect key sites including Buckingham Palace and the Houses of Parliament under Operation Temperer, triggered as a result of Britain's terror threat level being raised to "critical" - which has since been lowered.
Greater Manchester Police had arrested another man overnight on suspicion of terrorism offences as part of its ongoing investigation into the attack.
Early Saturday, two more men were arrested and taken into custody after officers carried out a controlled explosion to enter a home in central Manchester, police said in a statement.
A police officer, a police vehicle, and a bomb disposal unit wait outside a street in Moss Side, Manchester, Britain May 27, 2017.
At an emergency COBRA meeting, the independent Joint Terrorism Analysis Centre advised that the United Kingdom should return to the second highest level, which indicates an attack is highly likely rather than imminent.
Khan continued, "I encourage all Londoners to remain vigilant and report anything suspicious to the police". An address in the area was being searched as detectives sought members of a suspected terror cell behind named suicide bomber Salman Abedi.
Mark Rowley, the head of national counter-terrorism policing, said 17 searches had either concluded or were continuing - mostly in the North West. The Times newspaper reported on Saturday that intelligence officers had identified 23,000 extremists living in Britain.
However, Assistant Commissioner Mark Rowley, the United Kingdom police chief for counter-terrorism, advised people to be vigilant but to "go out as you planned and enjoy yourselves".
There are a number of high-profile events over the weekend including soccer cup finals in London and Glasgow, and the Great Manchester Run.
Greater Manchester Police described the evacuation in the inner-city area as a "precautionary measure to ensure everyone's safety".
The opposition Labour Party, emboldened by a rise in opinion polls, argued that Britain's foreign policy had increased the risk of attacks and criticized Conservative Prime Minister Theresa May for cutting spending on policing.