A ministry statement said the four were employees of the Bonatti construction company.
The kidnapping occurred Sunday evening and family members had been informed overnight, Foreign Minister Paolo Gentiloni said in Brussels, adding that intelligence agents were working to get more information on the circumstances of the kidnapping.
The ministry noted it had closed its embassy in Libya on Feb. 15 and urged Italians to leave the North African nation because of the dangers. Many Italians work in oil, gas and construction sectors in Libya, which was an Italian colony for much of the first half of the 1900s.
Libya has slid into chaos since the 2011 overthrow and killing of longtime dictator Moammar Gadhafi. It is now bitterly divided between an elected parliament and government cornered in the country's east, with little power on the ground, and an Islamist militia-backed government in the west that has seized the capital of Tripoli.
Foreigners are often taken hostage in Libya, either for ransom and of because of their Christian faith.
Some, like 10 Tunisian diplomats seized by gunmen from government-linked militias last month, were freed after demands were met. Last month, an Italian doctor kidnapped in January was also freed.
But others, like dozens of Ethiopians and Egyptian Christians who were seized by Islamic State extremists earlier this year, have been beheaded or shot dead in gruesome killings filmed and later broadcast by the group.
Most governments advise their citizens to avoid travel to Libya.
Hundreds of militias in Libya are aligned with either side or on their own, battling for power and turf in a lawless environment has allowed human traffickers and kidnappers to flourish. Libya is a huge gathering point for desperate migrants seeking to reach Europe and the smugglers who prey on them.
The U.N. envoy for Libya, meanwhile, has urged the Islamist-led government in Tripoli to sign a peace deal that would establish a unity government. Members of Libya's internationally recognized parliament, now based in the eastern city of Tobruk, and regional leaders initialed the unity accord in Morocco on July 11.
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