ANKARA (Reuters) - Turkey said on Sunday that six of its citizens were being held by eastern Libyan forces loyal to Khalifa Haftar, and that the militia would become a “legitimate target” if they were not released immediately.

Turkey supports the internationally recognized government in Tripoli, which on Wednesday pushed back eastern forces that have been trying for three months to seize the Libyan capital.

Ankara has also supplied drones and trucks to forces allied to Tripoli’s Western-backed prime minister, Fayez al-Serraj, while Haftar’s Libyan National Army (LNA) has received support from the United Arab Emirates and Egypt, according to diplomats.

“The detention of six of our citizens by illegal militia forces linked to Haftar is an action that amounts to banditry and piracy. We expect the immediate release of our citizens,” Turkey’s Foreign Ministry said in a statement. “If not, Haftar’s forces will become legitimate targets.”

On Friday, a spokesman for Haftar’s forces said they were banning commercial flights from Libya to Turkey and warned that any Turkish aircraft or ship attempting to land or dock in Tripoli would be treated as hostile. He also said the LNA would attack any Turkish military presence.

Earlier on Sunday, Turkish Defence Minister Hulusi Akar was quoted as saying any threats from Haftar’s forces would be punished severely, and that Turkey had taken measures to prevent attacks.

“As we contribute to establishing peace and stability in the region, any threatening stance or attacks will have a very heavy price, they will be reciprocated in the harshest and most effective way,” Akar was quoted as saying by state media.

Haftar and his backers say they are trying to free Tripoli from militias that they accuse of destabilizing Libya since the fall of Muammar Gaddafi in a NATO-backed uprising in 2011.

Haftar’s critics accuse him of trying to seize power through force and deepening a conflict between factions based in the east and west of the sprawling North African country.

Haftar’s offensive has upended United Nations-led plans to stabilize Libya after years of conflict that have left the oil producer divided and caused living standards to plummet.

The conflict risks disrupting oil production, creating a vacuum to be exploited by militants and prompting more migrants to head for Italy by boat.