"We have made sure that Nato military authorities are investigating the incident to bring full clarity to what happened," he said.

Turkish warships locked their weapons systems on to a French frigate called the Courbet, which was part of a Nato monitoring mission called Sea Guardian, on 10 June, according to France.

And they did it in order to slip through yet another illegal shipment of arms to Turkey's ally in the Libya civil war, the Tripoli-based Government of National Accord (GNA), France said.

"Turkey's support for the Government of National Accord's offensive goes directly against the efforts to secure a ceasefire, which we support," the French foreign ministry also said on Wednesday.

"This support is aggravated by the hostile and unacceptable actions of Turkish naval forces toward Nato allies," it said.

"This conduct, like all foreign interference in the Libyan conflict, must cease," it added.

And France had the support of eight other Nato countries against Turkey, the French defence minister, Florence Parly, told her parliament on Thursday.

The Courbet incident was the latest in a line of irritants between Turkish president Recep Tayyip Erdogan and his Western friends.

Others included: Erdogan's war on Kurdish people in Syria, illegal gas-drilling in Cypriot waters, Greek air-space violations, and abuse of migrants to destabilise EU borders.

But, at the same time, France's complaint on "foreign interference" in Libya must have looked like crocodile tears in the Nato talks.

Turkey might be violating a UN arms embargo, but, at least, it was fighting on the side of the EU and UN-recognised GNA.

Crocodile tears

Meanwhile, French special forces have been fighting alongside a warlord from eastern Libya, Khalifa Haftar, in a hybrid alliance involving also Russian mercenaries and African militias.

And if Turkey is to face a Nato inquiry about the Courbet incident, then France's ally, Haftar, also faces tough questions after a medical charity, the Red Crescent, last week, discovered mass graves in formerly Haftar-controlled zones, which the GNA had liberated with Turkish support.

French diplomats declined to speak to EUobserver about the blatant war crime.

But the French foreign ministry, earlier this week, told French media in Paris: "The discovery of mass graves in Tarhouna [a Libyan town] is deeply shocking".

"A thorough investigation must be conducted into this very serious matter and those responsible must be brought to justice", it said.

It remains to be seen how or if any Tarhouna probe goes ahead.

But Italy, the other main European power in the region, said on Wednesday: "In line with the recent statements of UN secretary general Antonio Guterres ... Italy calls for an independent and transparent inquiry in order to identify perpetrators and hold them accountable".

War crime

For his part, Stoltenberg did not mention Tarhouna on Thursday.

But he noted, in more general terms, that: "Nato, of course, supports the implementation of UN decisions, including UN arms embargoes".

"We also support the efforts of the UN to find a peaceful, negotiated solution to the conflict," he said.

The rival Libyan authorities, and their foreign backers, have been waging war for the past six years, in what has come to replace Syria and Ukraine as the most urgent crisis in Europe's neighbourhood.

But prospects of a "peaceful, negotiated solution" seemed dimmer than ever, with Italy, this week, also embedding military experts, to help clear mines, with the GNA-Turkey forces, multiplying the number of Nato divisions on the crisis and foreign boots on the battlefield.