The Embassy said in a statement on Wednesday that the former diplomat -- identified as Mohammad Fahim Kashaf -- entered the Embassy building a day earlier claiming that he had been named the Ambassador by Taliban militants, who seized power in Afghanistan in August last year.
The statement said Kashaf "attacked the Ambassador in the presence of an Embassy employee but the Envoy defended himself and called the police".
Kashaf was escorted out of the Embassy by the police, it added.
The Embassy in Italy, like many of Afghanistan's other diplomatic missions, remains in limbo with most staff still loyal to the Western-backed government toppled by the Taliban.
According to the statement, Kashaf had lost his job recently due to "lack of commitment to national values and the values of the Islamic Republic of Afghanistan".
The Islamic Republic of Afghanistan is the internationally recognised name of the country. The Taliban call the country the Islamic Emirate of Afghanistan, the report said.
In Kabul, Abdul Qahar Balkhi, a spokesman for the Foreign Ministry of the Taliban-led government, denied Kashaf's appointment as Ambassador, but also said that he had not been dismissed.
Balkhi said that the ministry's records showed Kashaf was appointed first secretary at the Embassy in Rome in December 2020, with a contract valid until December next year.
"But the ministry has also not appointed him as Ambassador of the Afghan Embassy in Rome. Kashaf's contract is valid, and his termination is illegal," Balkhi said in a statement, the report added.