Senior officers are encouraging people to go out but to remain vigilant on the first holiday weekend with the national threat level at its highest.
Security is being increased at football cup finals at Wembley and Hampden Park and the Great Manchester Run.
Police are now questioning 11 men over the attack in which 22 people died.
The latest arrests saw police detain two men, aged 20 and 22, after officers carried out a controlled explosion to gain entry to an address in the Cheetham Hill area of Manchester in the early hours of Saturday morning.
It came after searches at a separate property in Cheetham Hill and in the Longsight area of the city.
The UK threat level was raised from “severe” to “critical” following the suicide attack at Manchester Arena on 22 May.
The country’s leading counter-terror officer, Met Police Assistant Commissioner Mark Rowley, said on Friday that “immense” progress had been made in the investigation into a suspected network linked to suicide bomber Salman Abedi.
He said there were still “important” lines of inquiry to pursue but urged the public to “go out as planned and enjoy yourselves”.
Police had reviewed security at more than 1,300 events across the country and people could be “100% confident” they were doing everything possible to protect them, he added.
“Whatever events you are going to – whether you are going shopping or to sporting events or music events, I’d encourage the public to carry on. What they will see is many more police officers – some armed, some unarmed – out there to protect the public,” he said.
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About 1,000 armed police officers have been freed up by a decision to deploy the Army to protect key sites including Buckingham Palace and the Houses of Parliament.
Policing will also be stepped up at the Aviva Premiership Rugby Final at Twickenham and the football play-offs at Wembley on Sunday and Monday.
Met Police Ch Supt Jon Williams said operations will include both high-profile and covert tactics.
“All of this is designed to make the policing approach unpredictable and to make London as hostile an environment as possible to terrorists,” he said.
He added: “Anyone coming to the FA Cup Final or the other play-off matches over the weekend will see an increase in police numbers in and around the stadium.
“At Twickenham, rugby fans will see more armed officers on foot around the stadium.”