The names included Giuseppe Orsi, the chief executive of aerospace and defence giant Finmeccanica, the parent company of the targeted nuclear firm.

In a statement claiming responsibility for the shooting of Roberto Adinolfi, the Informal Anarchist Federation (FAI) said it wanted to strike Finmeccanica.

The FAI, which has also been behind a series of letter bombing campaigns in Europe in recent years, said it was preparing seven more attacks in honour of a total of eight fellow anarchist militants arrested in Greece.

Italian news agency ANSA reported that "seven or eight" industrialists had been assigned "40 or 50 bodyguards" and that a security committee of Rome's prefecture had also decided to deploy military personnel in strategic areas.

Italy has been on high alert ever since the shooting of Adinolfi, which was reminiscent of attacks against politicians, businessmen and trade unions leaders by far-right and far-left militants in the 1970s and 1980s.

Observers say the current financial difficulties facing many Italians could foment militant violence. Tax collection agency Equitalia in particular has been the target of violent protests in recent days.

Police and military forces found 6,250 kilograms (13,800 pounds) of plastic explosives buried in a jungle area where the rebels fought their final battles, police spokesman Ajith Rohana said.

"This is the biggest haul (on record) of explosives we have found," he said.

"The explosives, neatly packed in small bags, were buried near a bunker used by the LTTE (Liberation Tigers of Tamil Eelam)."

The guerrillas may have hidden the explosives for use against advancing government forces in the final days of fighting in May 2009, Rohana said, adding that there could be more hidden away in the area.

A senior military official, who asked not to be identified, said the discovery was made following a civilian tip-off.

"This quantity of explosives would be enough to blow up an entire town and we are surprised such a large amount was kept in one single place," the official told AFP.

Searches were carried out Sunday in the mangroves of Nandikadal where Tiger chief Velupillai Prabhakaran was reportedly killed by troops on May 18, 2009, and in the adjoining Puthukkudiriruppu area, police said.

Live ammunition for automatic assault rifles and hand grenades were found, as well as mortar bombs and landmines.

Security forces claimed victory over the rebels after killing Prabhakaran and his main military leaders in a no-holds-barred campaign. Since then there have been no attacks blamed on the rebels.

The Tigers, who during the height of their power controlled nearly a third of Sri Lanka's territory, were known for their trademark suicide bombings, which claimed high-profile targets including a president in May 1993.