Prisons in England and Wales are to receive £100m to improve security and cut crime, the government has said.
Airport-style security – such as X-ray scanners and metal detectors – would be introduced in more prisons, it said.
PM Boris Johnson said stopping weapons, drugs and phones getting into jails would prevent them becoming “factories for making bad people worse”.
But Labour accused him of “tinkering”, adding cuts had led to “unprecedented levels of violence in our prisons”.
It comes after Mr Johnson announced a programme to create 10,000 additional prison places and said the Crown Prosecution Service would receive an extra £85m over the next two years, to help deal with a rise in violent crime in England and Wales.
It also follows government initiatives for the NHS and immigration, which have sparked speculation about an early general election – although Mr Johnson has ruled one out before the Brexit deadline of 31 October.
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Announcing the extra money for prison security, Mr Johnson said the fresh investment was important because the public must “see justice being done, punishment being served and feel protected”.
Although most prisons already have some “airport-style” security controls, Mr Johnson said the extra money would be invested in struggling prisons – to help prevent drug smugglers from “fuelling a rise in violence and self-harm”.
January saw the number of assaults in prisons in England and Wales reach a record high. This number includes attacks by inmates on other inmates and those which target staff.
The Ministry of Justice said the £100m funding was newly-released by the Treasury and would be made available immediately.
It will fund an increase in “cutting-edge technology” to detect and “block mobile phones”, which criminals use to “organise drug supplies” or harass victims from their cells.
Justice Secretary Robert Buckland said there was a direct link between crime inside of prison and “crime on our streets”.
“This funding will have a transformative effect on prisons and give our hard-working officers the advantage as they tackle this scourge head-on,” he said.
“By disrupting those who continue to offend behind bars, we can keep our staff and other prisoners safe, and make sure that prisons truly fulfil their purpose of protecting the public.”
But shadow justice secretary Richard Burgon said the announcement fell “woefully short” of what was needed.
The Labour MP said Mr Johnson is “timidly tinkering at the edges” and blamed “reckless Tory cuts to staffing and budgets” for the “unprecedented levels of violence in our prisons”.
And Liberal Democrat justice spokeswoman Wera Hobhouse said it was a “hollow move” and that more money should be spent on rehabilitation to stop people committing crimes.
“Boris Johnson can lock people up for longer or search people on their way in and out of prison, but none of this bravado will actually make our streets safer,” she added.
In August last year, under former prisons minister Rory Stewart, the government promised to invest £10m to improve security and conditions in some of the worst prisons in England and Wales,
At the time, Mr Stewart pledged to improve conditions in 10 prisons which the Ministry of Justice said had “acute problems” with high drug use, violence and building issues.