Police in the UK have made three arrests in connection with Monday night's attack after an Ariana Grande concert.
It brings the total number of people being questioned to four.
GMP statement - Three men arrested— G M Police (@gmpolice)
The terror threat level in the UK has been raised from "severe" to "critical" in the wake of the Manchester bombing.
It's the highest possible rating, which means government and authorities expect another attack is imminent.
British Prime Minister Teresa May said a "wider group of individuals" could have been involved in the Manchester Arena blast rather than just a sole suicide bomber.
We all – every single one of us – stand with the people of Manchester at this terrible time.— Theresa May (@theresa_may)
Monday night's bombing after Ariana Grande's concert killed 22 people, including an eight year old girl. Dozens more were left injured.
A book of condolence for the Manchester attack victims will open at the Mansion House in Dublin from 10am today.
Elsewhere in the country, officials at Clare County Council and Kilkenny Town Hall are also offering people the opportunity to pay tribute.