Forces loyal to Gen. Khalifa Haftar and his Libyan National Army (LNA) seized a Jamaica-flagged Turkish cargo ship in the Mediterranean on Monday, angering the Turkish government and potentially reigniting the Libyan civil war after a tentative truce was established in October.

The LNA is the major rival to Libya’s internationally-recognized Government of National Accord (GNA). Haftar and the LNA came fairly close to capturing the GNA seat of power in Tripoli after a grueling extended siege last year but were repelled after Turkey intervened on behalf of the GNA. The feuding Libyan governments signed a ceasefire in October hailed by the United Nations as a permanent truce, although both sides retained their military positions.

On Tuesday, the LNA announced it had intercepted the Turkish cargo ship Mabruka the previous day and was investigating it for “violations of maritime laws and regulations.”

According to an LNA spokesman, the ship was bound for the port city of Misrata but entered a restricted area and did not respond to a challenge from naval forces. 

The spokesman accused Turkey of supplying the GNA with weapons and fighters in defiance of the ceasefire agreement, although he said no weapons were discovered aboard the Mabruka.

The LNA said the ship was towed to the port of Raas al-Hilal, while its 17 crewmembers — nine of them Turkish citizens — would be investigated for violating maritime regulations.

The Turkish foreign ministry demanded the immediate release of the ship and crew, as reported by Deutsche Welle on Tuesday:

The ministry said Haftar’s forces “continue their aggressive attitude” as the United Nations leads a political process in Libya aimed at elections next year. It warned of “serious consequences” if Turkish interests were targeted.

“In a period when the political process under UN auspices is underway between our Libyan brothers, Haftar and his militia are continuing their hostile stance,” the ministry said.

“Targeting Turkish interests in Libya will have grave consequences, and these elements [who target Turkish interests] will be viewed as legitimate targets,” it added.

A Turkish source told Reuters the ship was carrying much-needed “medicine and other medical products” shipped from Egypt to Libya.

“Patients who urgently need the medicines and blood products on that ship are waiting in Libya. It is clear that there are no weapons or anything else. Such seizures are not right,” the Reuters source said, accusing the LNA of using last month’s controversial German boarding of a Turkish freighter for possible arms embargo violations as an excuse to conduct its own searches.