Police investigating the murder of Sian O'Callaghan have found human remains at a field they are searching on the boundary of Oxfordshire and Gloucestershire, they said.

Detective Superintendent Steve Fulcher said the team from Wiltshire Police had been told they were those of a woman abducted in Swindon between 2003 and 2005. They have yet to be formally identified.

He also revealed that an examination of 22-year-old Sian's body, which was found at Uffington on Thursday afternoon, revealed she had not been sexually assaulted.

Sian's body was formally identified by her family on Friday night.

Supt Fulcher, speaking at a press conference in Swindon, said: "This morning officers have found remains which we believe to be human at the site at Eastleach."

He also said that while the 47-year-old man being held in connection with the two murder investigations had told them when a victim was abducted, he gave no indication of an exact time and date, or her identity.

"He indicated he killed a young woman between 2003 and 2005. He could not be specific about the date but he said she had been taken from the Swindon area."

Supt Fulcher also made a public appeal for anyone "lamping or poaching" in the area around Ramsbury, near Marlborough, in the early hours of Saturday last week, hours after Sian disappeared, to contact police without fear of arrest over their illegal activities.

News that the remains of a second person had been found came hours after police were granted a further extension by magistrates in Swindon to hold the man being questioned.

They have until 3.15am on Monday to question him further, before they must either charge or release him. He was arrested on Thursday after police swooped on a taxi rank at an Asda supermarket in Swindon. A green Toyota Avensis with taxi markings was also taken from the scene.

Police have been digging on Baxter's Farm, in the Cotswolds 17 miles from where Sian's body was discovered, since late on Thursday.