The three workers were arrested Saturday along with six Afghans from a hospital run by Milan-based Emergency in Lashkar Gah, the capital of Helmand province.
Emergency is one of the few foreign-run clinics in the city.
The nine were planning to conduct suicide attacks in the province, said Daud Ahmad, the provincial governor’s spokesman.
Authorities said the suspects had taken $500,000 from the Pakistan Taliban to launch their attack in a crowded location when Gov. Gulab Mangal was present.
Authorities found two suicide vests, two pistols and explosives hidden in medicine cartons at the clinic, Ahmad said.
Emergency has maintained a presence in Afghanistan for more than a decade, with its Lashkar Gah clinic treating more than 66,000 people, the group said.
In 2007, a hospital staffer mediated between the Afghan government and the Taliban to secure the release of kidnapped Italian journalist Danielle Mastrogiacomo.
Mastrogiacomo was freed but an Afghan translator, Ajmal Naqshbandi, was killed by militants.
Afghan authorities now say the three arrested Italians killed Naqshbandi.
The Italian government could not immediately be reached for comment.