The pledge to transfer them to secure training centres comes as prison inspectors called for girls to be removed from Holloway in north London.

A report by the Chief Inspector of Prisons, Anne Owers, said Holloway staff were not trained to deal with the girls, the premises appeared to be infested and the regime "grossly inadequate".

The YJB has said moves to remove all girls aged 16 and below from prisons are being frustrated by an increase in the numbers of teenagers being jailed.

We cannot carry on holding difficult and damaged children in situations where they are likely to be further damaged Anne Owers Chief Inspector of Prisons

Lord Warner, chairman of the Youth Justice Board, told BBC Radio 4's Today programme: "We [have] already provided in the last couple of years over 100 extra places for teenage girls outside the prison service.

"We will have completed the switch of all 16-year-old girls from the prison service, by the end of this year at the latest, to special units not run by the prison service at all.

"We are required by law to remand 17-year-old girls into prison service accommodation."

But he added it was difficult to expand the capacity to keep up with the increased numbers of girls jailed by the courts.

Cockroaches

All 15-year-old girls have already been removed from prisons.

A YJB spokesman said there was a shortage of places at supervision centres due to an increase in under-18 male inmates.

There's cockroaches all over the place and pigeons actually fly into your cells Elizabeth, former inmate

Click here for her account of life inside Holloway

That was due to Tony Blair's street crime initiative and Lord Chief Justice Lord Woolf's ruling on mobile phone theft, he added.

At Holloway, women inmates had poor access to showers and parts of the jail were plagued by cockroaches, the inspectors reported.

Staff suspected some units were also infested with lice and fleas, the report added.

Ms Owers told BBC Breakfast: "We cannot carry on holding difficult and damaged children in situations where they are likely to be further damaged.

"There are prisons which can give them better conditions than Holloway."

The inspection was made last July, when the prison held 12 girls aged under 18 and a further 53 young women aged 18 to 21.

I'm delighted that today's report recognised a lot of good things about Holloway which is a place I am absolutely certain is on the mend Martin Narey Prison Service

In total, there were 181 recommendations for improvements at the jail, although some areas such as drug treatment and the mother and baby unit were praised.

The director general of the Prison Service, Martin Narey, said improvements had been made amid a "significant change in culture" at the prison.

He said: "Holloway accepts juvenile prisoners because it has no choice - the YJB can offer no suitable places for them elsewhere."

Mr Narey said in some cases, teenagers had been through a range of community penalties and could receive the best service at Holloway, such as a detox programme.

Maxine Carr is at Holloway awaiting trial

Support group Women In Prisons said the root of Holloway's problems was simply overcrowding, with judges and magistrates jailing too many women for minor offences.

"We have a lot of people in prison who just shouldn't be there," spokeswoman Billie told BBC News Online.

Many female criminals turned to crime because of drug habits, debt and poor mental health, she said - which prison would only exacerbate.

"Prison is not hospital, it's not drug rehab, it's not drug therapy, it's punitive... do we want to solve crime or incubate it?"

Maxine Carr is at Holloway awaiting trial in connection with the deaths of the Cambridgeshire 10-year-olds Holly Wells and Jessica Chapman.