Powerful Libyan General Khalifah Haftar has ordered naval bases to confront any vessel entering the North African country's territorial waters without military permission.
A statement released by Haftar, the head of the self-proclaimed Libyan National Army (LNA), said that the command was directed to eastern bases in Benghazi as well as the capital Tripoli.
The warning by Libya's eastern commander comes after the Italian parliament authorized a naval mission to help Libya's coast guard curb refugee flows and reduce the number of people arriving on Italy's coasts.
Italy has reportedly begun the mission by sending a logistics ship and patrol boat as well as mechanics to maintain equipment.
Rome had initially hoped to send six ships into Libyan territorial waters, but the plans had to be scaled back following protests from Tripoli.
Italy's Defense Minister Pinotti earlier said that the vessels would only provide technical support and would not infringe on the North African country's sovereignty.
Italy maintains that it sent the mission upon request by the "UN-backed government" in Tripoli.
Libya now has two governments, one based in the capital, Tripoli, and the other based in the far east city of Tobruk. Haftar does not recognize the authority of the Tripoli-based Government of National Accord (GNA), instead backing an alternate government based in the country's east.
Libya has faced a power vacuum since a US-led military intervention resulted in the downfall of its longtime dictator Muammar Gaddafi in 2011. Since then, the country has been grappling with chaos and the emergence of numerous militant groups, including Takfiri terrorist group Daesh.
Some 600,000 mostly African migrants have reportedly arrived in Italy from Libya since the start of 2014.
Smugglers, exploiting the chaos in Libya caused by the 2011 uprising, pack desperate refugees and asylum seekers onto ill-equipped boats, which are usually intercepted by European vessels once they enter international waters.
Figures from the International Organization for Migration showed in mid-June that over 80 percent of the 60,000 refugees who have crossed the central Mediterranean route from Libya to Italy since January have set foot on the Italian territory, while more than 1,500 others have lost their lives in the rough sea.
Europe has been facing an unprecedented influx of refugees, most of whom are fleeing conflict zones in North Africa and the Middle East, particularly Syria. Many blame major European powers for the exodus, saying their policies have led to a surge in terrorism and conflicts in the Middle East, displacing the locals.