A minute's silence will be observed at 11am on Thursday, 25 May, in remembrance of those who lost their lives in the Manchester Arena attack.
At least 22 people were killed and more than 50 injured when Salman Abedi detonated an "improved explosive device" at an Ariana Grande concert on Monday night, as thousands of people were leaving the venue.
Twelve of the people killed were under the age of 16. Among the youngest victims of the bombing who have been named so far are eight-year-old Saffie Roussos, Nell Jones, 14, and Olivia Campbell, 15.
The minute's silence will mark the nation's solidarity with those injured in the attack - as well as everyone affected.
A vigil was held on Tuesday night in Manchester's Albert Square, attended by thousands.
A statement released jointly by 10 Downing Street, the Foreign Office and the Department for Culture, Media and Sport has said flags will remain at half-mast on government buildings until the evening of 25 May.
So far, seven people have been arrested in the UK over the attack as counter-terrorism police scrambled to uncover what is thought to be a significant terror cell linked to Abedi operating in the UK.