As the Greek police stepped up cooperation with its counterparts in other European countries in the wake of a barrage of letter bombs last week that managed to cross Greece's borders, reaching Germany and Italy, Kathimerini has learned that police in Italy had warned Greek authorities three years ago about the possibility of Greek guerrilla groups adopting the tactic of letter bombs, widely used by some Italian extremist groups. According to sources, the Italian police had informed their Greek counterparts in 2007 - during a regional security summit - of meetings and connections between members of Greek and Italian guerrilla groups. Greek police started communicating with their counterparts in Europe immediately after the first letter bombs were discovered early last week along with a list of embassies that proved to be the targets of bombs discovered over the next few days. A police source referred to «significant information that has been around for a while regarding the international connections of domestic terrorists seeking to gain know-how.» Last week, police sources said they were probing a suspected link between Greek and Italian extremist and anarchist groups, believed to be trading tactics. The police's interest in such a link was fueled by last week's letter bombs and the subsequent arrest of two young men, including a suspected member of Conspiracy of the Cells of Fire. In April 2008, the group issued a proclamation expressing admiration for the «revolutionary» tactics of its Italian «comrades» - a reference to letter bomb attacks by Italian extremists against police.