Prison suicides in England and Wales rose by 64% in 2013/14, according to the prisons complaints watchdog.

Ninety inmates took their own lives over the year compared with 55 the previous year, it found.

Nigel Newcomen, the Prisons and Probation Ombudsman, said the number of suicides was "a troubling reflection of the state of our prisons".

It also reflected "the level of mental ill health in prison" and failures to spot at-risk inmates, he said.

'Warning signs'

The ombudsman reported a big increase in self-inflicted deaths among adult male prisoners, with six suicides taking place among prisoners aged 18-21, an increase of four over the previous year.

But the biggest increase was among 25- to 30-year-olds, who accounted for 24% of suicides: there were 22 self-inflicted deaths in this age group compared with 14 the previous year.

There was also an increase in the number of prisoners taking their own lives during the first weeks and months of incarceration.

Mr Newcomen said there was only "anecdotal" evidence that the rise in suicides was caused by "stretched" prison resources.

He was unable to provide a "definitive explanation" for the rise in suicides, but cited some "sadly familiar issues" that were recurring, such as failure to take heed of warning signs that prisoners might be at risk of suicide.

"Complacency is not an option," Mr Newcomen said. "A rising suicide rate in prison reflects the state's difficulty in discharging its duty of care to some of the most vulnerable in its charge."

He recommended a review of the prison service's decade-old procedures on suicide and self-harm, given the examples found of "poor implementation" and the rise in suicides.

The ombudsman also reported four homicides during the year, twice as many the year before, and 130 deaths from natural causes.

The 7% rise in deaths by natural causes was largely explained by the fast growth of over-60s among the prison population, the watchdog said.