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

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, without specifying the location.

The Palestinian has been referred to the relevant judicial authority, the security forces said, and the authorities are looking for other people involved.

Lebanon has been heavily impacted by the civil war in neighbouring 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 jihadist presence there.