An increased risk of suicide in prison may be linked to staff shortages, a new report suggests.
Researchers quizzed former and current inmates about the issue after a rise in the number taking their own lives while behind bars.
The joint paper from the Howard League for Penal Reform and the Centre for Mental Health said: "Prisoners perceived a significant link between staff shortages and the increased risk of suicide.
"Prisoners with longer sentences or those who had been inside previously commented on the overall reduction in the number of officers, as well as a loss of experienced officers and personal officers."
It went on: "The reduction in the number of personal officers meant that staff did not have time to notice changes in prisoners' mood and interactions.
"This meant that signs of vulnerability increasingly went undetected."
Staff inexperience and lack of training around mental health were also seen as a significant factor in increasing risk, the report said.
It added that prisoners described a culture where "on the whole, distress was not believed or responded to with compassion".
It called for change across the system to recognise the influence of the prison environment on people's vulnerability.
Dr Graham Durcan, of the Centre for Mental Health, said: "With growing concerns about suicide in prison, it is vital that the experiences of prisoners are heard in devising solutions and reducing the risk of more tragic losses of life.
"Current and former prisoners are clear that good quality relationships are key to reducing the risk of suicide in prison. We also need to take action to reduce the risk of suicide among people leaving prison and provide 'through the gates' support at this critical time in their lives."
Andrew Neilson, Director of Campaigns at the Howard League for Penal Reform, said prevention of suicide in prisons is "an issue of grave importance".
Statistics published last month showed there were 100 apparent self-inflicted deaths in jails in England and Wales in the year to March - the highest level for more than 10 years.
The Ministry of Justice said staffing levels are kept under review and 2,830 prison officers have been recruited nationally since January last year - a net increase of 530.
A spokeswoman for the department said: "Every single day, dedicated prison staff provide support to thousands of prisoners at risk of self-harm or suicide, frequently saving lives through timely intervention.
"But as the Prime Minister said earlier this year, we must improve the way mental health problems are dealt with in the criminal justice system.
"The reforms announced in the Queen's Speech will empower governors to deliver the right health services for their prisoners. We will set out further plans in due course."