Italian police have opened an investigation after a threat letter with Arabic writing and bullets was delivered to a government minister. The message addressed to Justice Minister Andrea Orlando was signed "Isis", an acronym for the Islamic State group.

It contained two AK-47 bullets and a letter reading: "We will come to Rome and cut off your head. God is great," officials said. The address on the envelope had been written in English with a stencil, La Repubblica newspaper reported, adding that police sent it and its content for analysis.

Numerous lawmakers and officials expressed solidarity with Orlando. "Threats will not stop his commitment against terrorism," tweeted the speaker of the Chamber of Deputies, Laura Boldrini.

IS (Daesh) has often issued propagandistic threats against Rome and the Vatican, but Orlando had not been personally targeted before. The Islamist group usually makes threats through online statements or videos, while envelopes with bullets are the typical intimidation method used by the Italian mob.

The incident came as the Italian goverment announced it is to deploy troops to Iraq to defend a strategic dam from IS. Prime Minister Matteo Renzi said a 450-strong military contingent is to be sent to the war-torn country to secure the Mosul dam on the Tigris River, providing protection for an Italian firm that has secured a contract to repair it.