A suspicious package at the US embassy to the Vatican has turned out to be a false alarm. But US authorities have tightened security at their embassies.

An Italian anarchist group called the Informal Anarchist Federation is claiming responsibility for the parcel bombs sent to the Swiss and Chilean embassies.

Two staff members were injured from that incident. A third device was found at the Greek embassy, but did not explode. The embassy to the Vatican is in a different part of town from the much larger US embassy to Italy.

The incidents have prompted concern over a possible rise in violence by domestic European militant groups, exploiting mounting social tension.