Adolescents convicted of terrorism in England and Wales could receive a lifetime sentence by sentencing, which the government called the most radical in 20 years.
Currently, the lifetime tariff can only be given to people over the age of 21, but in exceptional cases such as terrorism, ministers plan to reduce this to 18.
A white paper outlining more details will be published this week.
But Labor said the Tories have pushed the justice system “to the brink”.
The proposals would include life sentences for those who kill children.
And there will be new powers behind the prison to prevent the automatic release of radicalized criminals while carrying out terrorism-related punishments.
Hashem Abedi, who helped his brother Salman plan the Manchester Arena bombings, has undergone planned reforms after being jailed for at least 55 years in August.
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He was less than 21 years old at the time of the murder so a life sentence was not an open option for the courts.
Sentencing Judge Jeremy Baker, Judge Jeremy Baker said a “life sentence” would be a “just sentence” in “exceptional circumstances,” but he said he would still “never be released.”
“It doesn’t matter if you’re just ’18, 19 or 20 ‘when you do this,” Boris Johnson, quoting Abedi’s case, wrote in the Sunday Express.
“We are setting a trap that will prevent some truly hateful offenders from being punished because they are under the age of 21 at the time of their crime,” Mr Johnson added.
“Dangerous criminals are not on our streets but behind bars – the only important principle of punishment with public punishment.”
Under the proposals, children between the ages of 15 and 17 who commit murder will also receive longer sentences.
Justice Secretary Robert Buckland said: “New measures to improve long-term imprisonment for dangerous offenders and re-cut correction – we’re providing an already well-equipped system to crack down on crime that the public can trust to keep them safe. “
But Shadow Justice Secretary David Lammy criticized the government, citing figures in a Prison Reform Trust report, which said the refund rate was 64% off for those who spent less than 12 months in prison.
Mr Lammi said: “We will examine this proposed law to make it as effective as possible, but we also ask ministers to hold their hands for their mistakes that have pushed the justice system to the brink.”
A white paper is expected to be published in mid-week before legislation is passed before parliament in the new year.
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