A half-marathon in Peterborough was called off following reports of a "man acting suspiciously", police have said.
The Perkins Great Eastern Run was due to take place on Sunday, but was cancelled 30 minutes after its original start time "in the interests of safety", event organisers said.
Cambridgeshire Police said its officers were called at 9.50am to reports of a man acting suspiciously on Alexandra Road, close to the event's route in Peterborough.
Police said information was passed to the race director who then decided to cancel the event.
In a statement, the race organisers said: "In the interest of safety for our participants we took the decision to cancel the half marathon half an hour after its original start time because of police information that a man was acting suspiciously close to the route."
Organisers said runners will be contacted next week to "confirm the process for the full refund of entry fees".
Thousands of people were expected to take part in the race, which was organised by Peterborough City Council and was due to start at 10.30am.
Those who were unable to take part can also defer their entry for the 2020 event, organisers said.
"We are disappointed, as we are sure you are. Thank you for your understanding," the race organisers said.
Last year's Perkins Great Eastern Run saw 3,452 people finish the race.
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