"It is with deep sadness that the Foreign Ministry confirms the death, today in Goma, of the Italian ambassador," the ministry said, adding that an Italian policeman also died.
In a separate statement, Foreign Minister Luigi Di Maio expressed his "great dismay and immense sorrow" and broke off from a meeting in Brussels with EU counterparts to make an early return to Rome.
"The circumstances of this brutal attack are not yet known and no effort will be spared to shed light on what happened," Di Maio said, paying tribute to the victims as "two servants of the state".
Attanasio was 43 and had been representing Italy in Kinshasa since 2017. He joined the diplomatic service in 2003 and served previously in Switzerland, Morocco and Nigeria.
According to the foreign ministry, the ambassador and the policemen were part of a convoy of MONUSCO, the UN peacekeeping mission in Congo.
A diplomat in Kinshasa told the French news service AFP that Attanasio was with a convoy of the UN's World Food Programme (WFP) when it came under fire near Goma.
A spokesman for the Rome-based WFP could not confirm this, but told AFP the organisation was looking into the reports.
