The Belfast Trust has apologised "unreservedly" to patients and families affected by allegations of ill-treatment at a County Antrim hospital.
The trust is to complete an investigation following the suspension of further staff from Muckamore Abbey.
The hospital provides care to adults with an intellectual disabilites, behavioural or mental health problems.
On Thursday, the Belfast trust confirmed that a further nine members of staff had now been suspended.
In a statement, it said: "We are in the process of meeting with the families so that we can apologise to them directly, and to explain in further detail the actions we are taking.
"We wish to assure all of the patients who we care for in Muckamore Abbey Hospital and their families that their safety is our absolute priority at all times."
An adult safeguarding investigation was initiated in September 2017 following reports of inappropriate behaviour and the alleged physical abuse of patients by staff in two wards in the hospital - one of which was the Psychiatric Intensive Care Unit.
The statement said the trust "took swift action and suspended four members of staff" at that time.
It added: "Since then, we have put in place enhanced arrangements to ensure high standards of care are maintained.
"As part of the ongoing investigation and a review of archived CCTV footage, a further number of past incidents have been brought to our attention in the past week.
"Due to the serious nature of this evidence, we have taken immediate action to suspend nine staff - the majority of whom are nurses - and we are currently in the process of interviewing ten further staff who were reported to us as witnesses to these events."
The trust has secured the services of an expert panel - which includes a carer - to independently review the standard of care in Muckamore Abbey Hospital.
The statement added: "This regrettable and unacceptable situation in no way reflects the work of our 500 dedicated and professional staff who provide excellent care every day to the 80 patients in Muckamore."
Director of the Royal College of Nursing in Northern Ireland, Janice Smyth, told BBC News she is worried about both staff and patients at the hospital.
"They [the patients] are amongst the most vulnerable. It's very important that they have continuity of care, that's there a stable nursing workforce there to look after them, that their quality of life is as good as it can be," said Ms Smyth.
"Those are issues that are a huge concern to us, but we're also very concerned about the health and wellbeing of the staff who work there.
"As you can imagine, this has been a significant burden and concern for nurses and other staff working there since September last year."
The PSNI confirmed that its investigation is ongoing.