A half-marathon was cut short as participants waited to start because of a "suspicious vehicle" on the route.
About 11,000 runners in the queue for the Great Birmingham Run were told that wet weather had forced organisers to reduce the distance by a mile.
But organisers later said that the changes were made after talking to police about a safety threat in the Cannon Hill Park area.
Organisers apologised for the changes but said safety was their priority.
The vehicle was subsequently declared safe.
It came on the same day as a security incident in Peterborough in which a half marathon was called off as armed police responded to reports of a "suspicious" man.
In Birmingham the planned course, starting on the city's New Street, was due to take runners through Cannon Hill Park at the nine-mile mark, before finishing near to Aston University's campus.
But runners said the route was even shorter than expected as they were diverted away from both the park and Edgbaston's cricket ground, clocking up "just over 11 miles".
James Liddiard, from Birmingham, said: "It was a really strange race because you didn't know how far you were going to be running. After the eight mile mark we didn't see another one until 12. "I'm a bit deflated as it's not what we signed up for.
Some participants took to social media to call for a refund.
David Cox branded the run a "total farce", with "incompetent" planning.
Laura Gent said runners needed to respect the decision to keep everyone safe.
"It's annoying that the time won't count but it's still good training and it's not a pointless run just because it's not 13 miles," said Ms Gent.
The Great Run race organisers said in a statement that the route was reduced, after consultation with police, to avoid Cannon Hill Park and Edgbaston.
"We can assure participants and spectators that their safety was not compromised at any point," the spokesperson added.
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