The Care Quality Commission has issued a formal warning to Avon and Wiltshire Mental Health Partnership over levels of staffing at Blackberry Hill Hospital in Bristol.
It followed an unannounced inspection of three wards at the Fromeside Unit in December. The medium secure unit provides specialist care and treatment for adults with mental disorders, which may mean that they are at significant risk of harming themselves or others.
Inspectors found that the unit was failing to comply with the national regulation on staffing and did not have not enough qualified, skilled or experienced staff to meet people's needs.
More top news
Becky Watts' uncle speaks exclusively to ITV News following the arrest of two people on suspicion of her alleged kidnap and murder.
The killer serving life for the murder of Jo Yeates has been sentenced to a further 10 months after admitting possessing child abuse images.
Meet the twins from Gloucester who've had to produce their birth certificates to friends in order to prove that they are in fact related.