A local post office was targeted and a female shopkeeper attacked during a series of raids on Monday.
The outlet in Kincardine was one of four targeted across Fife and West Lothian.
At around 12.15 pm in Cowdenbeath High Street a man attempted get behind the counter area but was refused access and left the premises.
Shortly after, at about 12.40 pm, he entered Burntisland Post Office carrying a knife and made off with a four-figure sum of money before staff contacted police.
Officers were then alerted to a third incident at the post office in Elphinstone Street, Kincardine, which occurred around 2.15 pm. A man in possession of a weapon entered and assaulted the female shopkeeper before making off with cash.
Given the circumstances of the crimes officers are considering a link to an earlier theft in Linlithgow. At around 11.25 am, a man entered and stole a sum of cash from the till.
The suspect in each incident is described as white, in his 30s with a stocky build, stubbly complexion and wearing dark clothing and a high-visibility jacket.
Detective Inspector Colin Robson said: “These incidents were all extremely alarming for the staff involved and we are providing each of those affected with all the support they require will they assist us with our ongoing inquiries.
“We believe the same male was responsible for each of these crimes and would ask that anyone who can help us to identify this individual contacts police immediately.
“Anyone with any other information relevant to this investigation is also urged to get in touch.
“We are also working closely with Post Office Counters with a view to raising awareness and prevent further crimes.”
Those with information can contact Police Scotland on 101 or the charity Crimestoppers on 0800 555 111.