An "urgent" inquiry has been demanded after a dummy bomb used in a security exercise caused a Premier League match at Old Trafford to be postponed.
The game between Manchester United and Bournemouth was called off after the item was discovered close to kick-off. A controlled explosion was carried out on the device, which police said was accidentally left by a private firm.
Greater Manchester Mayor and Police and Crime Commissioner Tony Lloyd called for a full inquiry into the "fiasco".
Bomb disposal experts were called to the 75,000-seat stadium on Sunday after the replica device was found in a toilet.
The Premier League match has since been rearranged for Tuesday at 20:00 BST.
Lloyd called the situation "unacceptable" and demanded an urgent inquiry to discover "how this happened, why it happened and who will be held accountable".
He added: "This fiasco caused massive inconvenience to supporters who had come from far and wide to watch the match, wasted the time of huge numbers of police officers and the army's bomb squad, and unnecessarily put people in danger."
The Premier League also thanked all concerned for how the matter was dealt with.
A statement read: "We would like to thank Manchester United's staff, the police and other emergency services for all their efforts today as well as rearranging the match for this coming Tuesday.
"Both Manchester United and AFC Bournemouth's management has been extremely helpful in reaching a swift resolution, which is the best possible given today's events."
United will refund all tickets and allow ticket holders from both clubs in for free on Tuesday.
Manchester United season ticket holders will also be given a credit.
It is estimated this gesture will cost United around £3m.
Bournemouth expect to make an announcement on arrangements for their travelling fans on Monday.
A Greater Manchester Police (GMP) statement read: "Shortly before today's planned football fixture, staff from the Manchester United ground alerted police to a suspicious item that had been found in the toilets within the North West Quadrant, between the Sir Alex Ferguson stand and the Stretford End.
"Police quickly attended and explosive experts were called in to assess the item, which has been described as an incredibly realistic-looking explosive device."
The Sir Alex Ferguson Stand and the Stretford End were evacuated and sniffer dogs brought in.
Kick-off was delayed initially and shortly afterwards the match was abandoned on police advice.
A bomb disposal team carried out the explosion at about 16:30 BST.
Assistant chief constable John O'Hare said: "I am grateful to the Manchester United and Bournemouth supporters for their support and assistance today.
"Following today's controlled explosion, we have since found out that the item was a training device which had accidentally been left by a private company following a training exercise involving explosive search dogs.
"While this item did not turn out to be a viable explosive, on appearance this device was as real as could be, and the decision to evacuate the stadium was the right thing to do, until we could be sure that people were not at risk."
Manchester United's executive vice-chairman Ed Woodward said: "The club takes security very seriously and staff are regularly trained with the police and emergency services to identify and deal with these incidents.
"We will investigate the incident to inform future actions and decisions
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