The four men, among whom only one is in custody, had planned to “assassinate former U.N. chief Ban Ki-moon during his 2013 visit to Lebanon and his inspection of U.N. forces operating in south Lebanon (UNIFIL),” the National News Agency said.

They were also charged with “attempting to poison water tanks used by the Lebanese Army to kill the biggest number of soldiers and also with plotting a terrorist operation in the Sardinia region in Italy.”

Germanos referred the file to First Military Examining Magistrate Riad Abu Ghayda, demanding “the interrogation of the detainee, the issuance of an arrest warrant for him, and the issuance of three in-absentia arrest warrants for the three fugitives.”

The detainee, born in 1991, admitted to links with an IS member in Syria "who tasked him with making explosives and concocting poison," General Security said in a statement on Thursday.

He prepared to "concoct a quantity of deadly poison along with someone living in a foreign country" for two planned poisonings.

The first was to "poison one of the water tanks from which the Lebanese Army's trucks fill up on water every day to take it to the army barracks."

The second was to "carry out a mass poisoning in a foreign country" through "poisoning food during a public holiday," the statement said, apparently referring to Italy's Sardinia.

Lebanon has been heavily impacted by the civil war in neighboring Syria since it erupted in March 2011.

Security forces have on several occasions arrested suspected IS members. They are usually tried by military courts, but their trials have dragged on due to the amount of cases.

Lebanon has been rocked by several suicide bombings since 2013, some of them claimed by IS. The extremist group in August last year evacuated a Lebanese-Syrian border region under an unprecedented deal to end three years of IS - Daesh presence there.