A man seen approaching children on several occasions near a Dorset army base is being sought by police.
He was spotted in an isolated spot on Ministry of Defence land between Swinton Avenue and Holt Road in Bovington in June, July and August.
The incidents were reported by two members of the public.
There have since been two further sightings of him, prompting a police search of the area involving the force helicopter, dogs and patrol officers.
A Dorset Police spokesman said the force was working with the Ministry of Defence Police.
The man was seen approaching children on 22 June, 31 July and 11 August and since then there have been two further sightings.
The spokesman said police were "keeping an open mind" and had not confirmed whether all the incidents were linked.
Det Insp Jim Beashel said: "We are treating these incidents extremely seriously, as it is not yet known what the man's motives may have been."
He said police patrols have been stepped up in the area, which is isolated and popular with dog walkers.
"I would actively encourage anyone who has any information regarding these incidents, and anyone who notices any suspicious activity in the area, to contact us," Det Insp Beashel said.