Italian police have discovered a massive international paedophile network selling violent child-pornography videos to clients in Italy, the US and Germany.

Eight Italians have been arrested and 490 warned that they are under investigation, in a scandal that has shocked and outraged the country. Police are reportedly trying to identify 5,000 people who are suspected of attempting to purchase the videos, some of which appear to contain images of children being tortured and murdered.

The tapes, which were made in Russia, have allegedly generated revenues of £410m for their makers.

The directors of two state-run television news programmes resigned yesterday after brief excerpts of the paedophile videos were broadcast on Wednesday to illustrate reports. The images were apparently taken from internet sites promoting the pornographic films, which cost anything from £270 to £4,000.

Gad Lerner, the respected director of the main RAI One news programme, interrupted his broadcast to apologise to viewers for the "ignoble" and "violent" images that had been shown only minutes earlier.

Mr Lerner and his RAI Tre counterpart, Nino Rizzo Nervo, admitted that they did not know what was going to be on the reports.

Italian investigators have identified three Russians who are suspected of being at the heart of the traffic in violent films, which are promoted over the internet and distributed on video cassettes, CDs and DVDs.

One of them, Dimitri Ivanov, has reportedly been in prison since September 1999, charged with violence against minors and the distribution of pornographic material. The other two, Dimitri Kuznetsov and Andrei Minaev, are said to have benefited from an amnesty passed by the Russian parliament.

The investigation began two years ago following a denunciation by a parish priest from the Sicilian town of Avola, who runs a helpline for abused children. He found evidence of the traffic on the internet.

Italian police identified the internet site that promoted the videos and intercepted 3,000 cassettes before they reached purchasers in Italy.

The investigators named the Russian firms involved in the trade as Tim-O-Seev Video and Flower 2. Many of the tapes were duplicated and delivered to buyers by police who posed as postmen. Those arrested include businessmen and public employees.

Exposure to the images has been a traumatic experience for police and magistrates. Alfredo Ormanni, the prosecutor in Torre Annunziata, near Naples, who is coordinating the inquiry, said they induced such a sense of desperation that he had been tempted to abandon his profession.

"For some time it has been possible to buy the sound files of rapes and every time that we discover one and report it to the police the screams of those children remain in my brain for days, and I blame myself for not being able to save them," said Father Fortunato Di Noto, whose denunciation began the investigation.

Investigators said they believed that the victims shown in the films were kidnapped from orphanages in Russia and the Middle East. Some are said to have been snatched from their parents during visits to the circus.