The disappearance of a woman and her two-year-old daughter is being treated as a murder investigation, police said.
A 50-year-old man has been arrested and charged in connection with the deaths of Bennylyn Burke, 25, and her daughter Jellica, from South Gloucestershire.
Officers are still searching for their bodies.
A second child who was reported missing with the pair has been found and is being supported, Police Scotland said in a statement.
Detective Superintendent Graeme Mackie said: “We are now treating the disappearances as a murder investigation and I would urge anyone with any information to please come forward and speak to us.
“This is a complex enquiry involving both local officers in Dundee and specialist resources from across Police Scotland.
“Bennylyn’s next of kin have been updated on the arrest and are being supported by colleagues from Avon and Somerset Police.
“Our thoughts are with her family and friends at this very difficult time.
“There will be an increased police presence in the area for a considerable period of time and I would like to thank the local community for their cooperation.”
Ms Burke and her two children were reported missing on 1 March, prompting Avon and Somerset Police to issue an appeal for information two days later.
She was last seen at her home in south Gloucestershire on 17 February, according to police.
On Friday afternoon officers raided a house in Troon Avenue, Dundee and arrested the suspect. He is due to appear at Dundee Sheriff Court on Monday.
Police and forensic officers were still at the scene in Troon Avenue on Saturday.
Det Supt Mackie asked anyone with information to speak to local officers or to call Police Scotland via 101.