Prison safety in England and Wales has "deteriorated further" and urgently needs improving as figures show escalating self-harm, violence and disorder, a group of MPs has said.
The number of self-inflicted deaths in prisons rose by 26% - from 79 to 100 - in the 12 months to March, according to a report by the Justice Committee.
Its chairman Bob Neill said prison safety was a matter that "cannot wait".
Prisons minister Andrew Selous said improvements were being made.
The report found:
- Serious assaults increased by 31% - from 2,150 in 2014 to 2,813 in 2015
- General assault incidents rose by 26% from 14,069 in 2014 to 17,705 in 2015
- There were 1,935 fires in adult prisons and young offender establishments in 2015 - a 57% increase on 2014
The committee said the prison service has a "major issue" with staff retention, which resulted in a net gain of only 440 prison officers in 2015 following the recruitment of 2,250.
The MPs also said there were currently 7,000 fewer officers than in 2010, when the prison population was 2,500 lower that it is now.
The committee did however recognise that the Ministry of Justice and the National Offender Management Service (Noms) had sought to improve safety by creating offences for the possession of new psychoactive substances and knife possession in prison.
Body-worn cameras and to improve safeguarding procedures have also been introduced.
But "overall levels of safety in prisons have not stabilised as the ministry hoped, let alone improved and continue to deteriorate significantly", the report said.
Mr Neill called for the government to urgently draft an action plan aimed at increasing safety levels for both staff and prisoners.
"It is imperative that further attention is paid to bringing prisons back under firmer control, reversing recent trends of escalating violence, self-harm and disorder," he said.
The committee also highlighted the death of custody officer Lorraine Barwell, who died after being kicked in the head by a prisoner in July 2015, as an example of the worsening situation.
'Places of decency'
Mr Selous said "we must do better" at reducing violence and self-inflicted deaths and stopping drugs getting into prisons, as well as doing more to help prisoners with mental health problems.
"This report demonstrates the very serious challenges facing the prison service and shows how badly prison reform is needed," he said.
"We have secured £1.3bn to modernise the prison estate and we have responded to staffing pressures with a national net increase of 530 officers, since January last year.
"These reforms will ensure prisons are places of decency and improve public safety by reducing reoffending."