Police who staged a mock attack featuring a bomber shouting "Allahu Akbar" have been forced to apologise for stereotyping.
The exercise - criticised for using a fake "Muslim terrorist" - was to test the response of emergency services.
Eight hundred volunteers took part in the overnight drill to make it as realistic as possible.
Greater Manchester Police said the event at the Trafford Centre was not linked to any specific terror threat.
Manchester peace activist Dr Erinma Bell criticised the use of a "Muslim terrorist".
She said "a terrorist can be anyone" and "we need to move away from stereotypes".
In a statement released by GMP, assistant chief constable Garry Shewan said: "It is a necessity for agencies including the police to train and prepare using exercises such as this, so that we would be in the best possible position to respond in the event that the unthinkable happened and an attack took place.
"The scenario for this exercise is based on an attack by an extremist Daesh-style organisation and the scenario writers have centred the circumstances around previous similar attacks of this nature, mirroring details of past events to make the situation as real life as possible for all of those involved.
"However, on reflection we acknowledge that it was unacceptable to use this religious phrase immediately before the mock suicide bombing, which so vocally linked this exercise with Islam. We recognise and apologise for the offence that this has caused."
Mock horrific injuries
Armed officers drilled their counter-terror tactics during the simulated attack at the entrance to The Orient food court.
It started at midnight when a man dressed all in black walked in shouting.
An explosion then rocked the food hall and volunteers - wearing ear defenders and safety glasses - who dropped to the floor.
Many were made up to look as if they had sustained horrific injuries and others screamed out as if in pain.
Smoke filled the entrance to the food court and some of the volunteers ran from restaurants, as if they were trying to dash to safety.
GMP said the simulation - codenamed Winchester Accord - was to "test the emergency response to a major terrorist incident".
Greater Manchester's police and crime commissioner Tony Lloyd, said: "The public expects the highest standard of training where all of our emergency services locally work together effectively with those with national responsibility to keep the UK safe.
"This planning event has helped ensure that should the unthinkable ever happen, Greater Manchester will be ready.
"However, it is frustrating the operation has been marred by the ill-judged, unnecessary and unacceptable decision by organisers to have those playing the parts of terrorists to shout 'Allahu Akbar' before setting off their fake bombs.
"It didn't add anything to the event, but has the potential to undermine the great community relations we have in Greater Manchester."
GMP said the event had been planned since December and some of the three-day training exercise will take place in Merseyside.
Other locations in the counter-terrorism exercise include Redbank Community Home in Newton-le-Willows on Wednesday.