Global mail and parcel services stopped for 48 hours after series of mail bombs were sent from the country.
Separate blasts at the Chilean and Swiss embassies in Rome, the Italian capital, have wounded two people, Italian police say.
The blast at the Chilean embassy came just hours after the explosion in the mailroom of the Swiss mission on Thursday. Both of the injured were wounded while opening the packages.
A third suspect package was found at the Ukrainian embassy, but was did not appear to contain explosive materials, Yevhen Mitskevich, an embassy spokesman, said.
Police are now checking all embassies in the capital for dangerous materials.
Gianni Alemanno, Rome’s mayor, referred to the blasts as a “wave of terrorism against embassies” and said this was “much more worrisome than a single attack”.
“We are working with bomb disposal experts to ensure that no packages can be opened by inexperienced people,” Francesco Tagliente, Rome’s chief of police, told the Reuters news agency.
Reports said that claims of responsibility from an Italian anarchist group had been discovered at the Chilean embassy, although they have not been confirmed.
ASNA, the Italian news agency, said that a claim of responsibility by anarchists was discovered in a small box near one of the injured embassy employees, and was being examined by an anti-terrorism police squad.
Al Jazeera’s Sabina Castelfranco, reporting from Rome, said there was an idea that anarchists could be behind the bombs “but the information is very very sketchy at the moment”.
“Investigators say it could be anarchists, the Rome mayor said that it’s probably not domestic, that they are following an international lead,” she said.
“But really it is too early to establish who is behind this.”
The blast at the Swiss embassy seriously injured one man working in the mailroom, authorities say.
He was taken to hospital with wounds to his hands, which were caused when he opened the package at around midday (1100 GMT).
The diplomatic mission is situated in a prosperous part of the Italian capital, where many foreign embassies are located.
“The ambassador is still on site, the embassy has not been evacuated,” Maurizio Mezzavilla, the head of the Carabinieri police force in Rome, said at the Swiss embassy.
In a statement, Franco Frattini, the Italian foreign minister, said: “We express our full solidarity with the Swiss ambassador and with all the personnel of this diplomatic representation, which has been the target of a deplorable act of violence that deserves our strongest condemnation.”
A rudimentary device was discovered in an empty underground train in Rome on Tuesday.
However, police said that the device lacked a detonator and tests showed it contained no explosive.