Italy was on alert for new attacks on Friday, a day after an anarchist group claimed responsibility for parcel bombs that injured two people at the Swiss and Chilean embassies in Rome.
There was a false alarm on Friday at the Irish embassy, when police were called to open a package that resembled those sent on Thursday, but which turned out to contain a greeting card.
Investigators have noted the past fondness of anarchist splinter groups for attacks over the Christmas period and have said that more are likely and Italian embassies abroad have been put on alert. But authorities have otherwise said little.
"The investigation is under way, there's no other information for the moment," a Rome police spokeswoman said.
Cesar Mella, the Chilean embassy worker injured when one of the packages exploded in the mailroom, lost two fingers and suffered other injuries, while Andreas Clemens, a Swiss staffer, had fractures and other injuries to the hands, arms and body.
Apart from the two men's injuries, Thursday's attacks caused relatively little damage. But they underlined fears of a resurgence in far-left militant violence at a time of growing social tension over spending cuts across Europe.
Still, there was no indication of any link with student protests in Rome last week that spiralled into some of the worst violence seen in the Italian capital in years.
The group claiming responsibility for Thursday's attack, the Informal Anarchist Federation (FAI), is well known to Italian police and was described in an intelligence report to parliament last year as "the main national terrorist threat of an anarchist-insurrectionist type".
It gained notoriety in 2003 with its so-called "Santa Claus campaign" against EU institutions which included a parcel bomb sent just before Christmas to Romano Prodi, a former prime minister who at the time was head of the European Commission.
Compared with the bloody campaigns of assassinations and kidnappings in the 1970s by groups such as Germany's Red Army Faction or the Red Brigades in Italy, far-left violence has been a relatively minor phenomenon in Europe in recent years.
But a climate of tension amidst austerity measures that have hit public services during the financial crisis has raised fears that extremist groups may try to exploit protests, above all in countries like Greece where cuts have been most severe.
EU authorities say far-left attacks remain a limited threat but they have more than doubled in number since 2007, mainly targeting government and business interests and concentrated most heavily in Greece and Spain.
Italy has a history of leftist violence and the FAI last year claimed responsibility for an attack targeting the director of the centres where illegal immigrants are detained before expulsion, and for another on Bocconi University in Milan.
Italian media reports also highlighted a possible connection with the cases of Costantino Ragusa, Silvia Guerini and Luca Bernasconi, three far-left militants arrested and detained earlier this year near an IBM facility in Switzerland.
The magistrate who investigated the attack on Prodi estimated the membership of the FAI, which is unrelated to the Italian Anarchist Federation whose initials it shares, at around 350 but said it was extremely difficult to pin down.
He said at the time that it was made up of "individualists who don't accept any type of organisation, structure or centralisation of decision-making".
In a message found by police with the package sent to the Chilean embassy, the group said it wanted to strike a blow against the political system but made no specific demands.
"We have decided to make our voice heard with words and with facts, we will destroy the system of dominance, long live the FAI, long-live Anarchy," said the note, written in Italian.