Hacker groups have said they had accessed the website of Italy's cyber police and published classified information online in revenge for arrests of hackers in Europe and the United States.

The communications police unit admitted it had been hacked but did not confirm or deny that any information had been stolen, while lawmakers condemned an "unprecedented" attack that had breached Italy's security.

The attack dubbed Operation Italy "revealed some of the most important and most secret reports of the cyber police on illegal and immoral practices," hacker groups LulzSec and Anonymous said in a statement on a blog on Monday.

The leaked reports "will show abuses committed in Europe by the CNAIPIC (National Centre against Cyber Crime and for the Protection of Critical Infrastructure)," they said on the site http://anonops-ita.blogspot.com.

The information published by the hackers so far consists of eight megabytes of documents on a variety of Italian government interactions with ministries and business groups in Australia, Belarus, Egypt, Russia and Ukraine.

Hackers said the documents represented only one per cent of the total cache. "We are working to try to understand the scale of what happened," the police unit said. "We have to verify if documents have been taken and which ones."

Emanuele Fiano, a lawmaker from the opposition Democratic Party, said: "This cyber attack against the police task force is of an unprecedented gravity."  He said he would propose new legislation to crack down on hackers "in order to improve this fundamental aspect of our country's security."

Another Democratic Party deputy, Ettore Rosato, said the attack was "very worrying," adding: "We are waiting to hear about the files published by the hackers. If they are originals, this is an act of unprecedented seriousness."

CNAIPIC was set up in 2008 with the aim of cracking down on cyber crime. The attack comes after Anonymous and LulzSec vowed Thursday to continue their struggle for transparency, two days after a series of arrests.