Germany has rejected protests from Ankara over an inspection by its naval officers of a Turkish ship sailing off the Libyan coast. 

German forces, acting under the European Union's "Irini" directive – aimed at blocking arms smuggling to Libya – were forced to abandon their operation when Turkey complained to Berlin over what it called "heavy-handed tactics."

The incident on Sunday occurred when German marines boarded the ship, the Roseline A, 200 kilometers north of Benghazi. Turkey has released CCTV footage appearing to show crew members being led away by uniformed naval officers with their hands behind their heads. Ankara said troops on the German frigate Hamburg violated international law by boarding without permission. Germany responded claiming its forces acted after four hours had passed with no reply to a formal request for an inspection.  

Speaking on Tuesday, Germany's defense minister, Annegret Kramp-Karrenbauer, said the unit, "behaved correctly and acted absolutely in line with the mandate of the European mission. That there is this debate with the Turkish side points to one of the fundamental problems of this mission." 

Kramp-Karrenbauer went on to state: "It is very important to me to say clearly here that there are no grounds for these accusations that are now being made against the soldiers."

Turkey insists the vessel was carrying humanitarian aid to Libya, which is now in its sixth year of civil war following the collapse of the Gaddafi regime, pointing out that nothing suspicious was found aboard the 16,000-ton container ship.  

The Turkish Foreign Ministry summoned EU, German and Italian envoys to Ankara following the incident, which it said in a statement, "was conducted without authority and with the use of force." Condemning the operation, Turkey's defense minister, Hulusi Akar, said Ankara was working on new measures to protect Turkish commercial vessels in the Mediterranean Sea.

Turkey has backed the elected government in Tripoli throughout Libya's ongoing bloody civil war, against forces loyal to rebel leader Khalifa Haftar, a stance that has brought it into conflict with other NATO members, notably France. Earlier this year, the EU's high representative on foreign affairs, Josep Borrell, complained of "blatant violations" of the United Nations-backed arms embargo on Libya by countries that had previously agreed to observe the international ban on the supply of weapons to the country.

This latest spat with a fellow NATO member comes at a time when relations between Turkey and the EU remain tense. The bloc has clashed with Ankara over several issues, including drilling for natural gas by Turkish ships in disputed territory in the eastern Mediterranean, Turkey's military campaign in Northern Syria and concerns in Brussels over Turkey's role in the recent elections in Northern Cyprus. 

In a statement, the German foreign ministry said Berlin took the Roseline A incident "very seriously," and reminded all participants in the Libyan peace process of the need to adhere to the terms of the arms embargo.