Paedophiles soliciting explicit photographs from children on mobile phones or online will face up to two years in prison as the government plans to close a loophole in the law.
Prime Minister David Cameron will reveal details of the new sexual communication offence at a Downing Street summit today.
It is already illegal for an adult to exchange sexual pictures with anyone under the age of 16, but there is no specific law against requesting explicit images.
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The new law will target paedophiles "fishing" for victims online. Anyone over the age of 18 will be banned from talking about sex to a child under the age of 16 on a chat room, from sending explicit text messages or inviting them to communicate sexually.
Cameron has described the new measures as a "watershed moment" in reducing the volume of child abuse images online.
He tells the Daily Mail: "We have seen an increasing and alarming phenomenon of adults grooming children online, encouraging them to send images of themselves.
"There can be no grey areas here. If you ask a child to take their clothes off and send a picture, you are as guilty as if you did that in person."
So-called "revenge porn" and possession of material offering guidance on abusing children will also be made illegal, while GCHQ and the National Crime Agency will be given more powers to target abusers sharing internet content.
The two agencies are expected to work together to tackle serial offenders using encrypted internet networks known as the dark net to hide from justice.
The new measures will be introduced through the Serious Crime Bill currently going through Parliament.
Experts from more than 50 countries and 23 leading technology companies will attend the We Protect Children Online summit.
Cameron is expected to announce new technology from Google that can identify and block known child abuse videos, as well as new solutions developed by other technology companies to track down offenders.
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