The German government on January 25 faced calls to halt arms exports to Turkey after it emerged that German-made Leopard tanks were being used in Ankara’s Afrin offensive against the Kurdish YPG.

Some German politicians on both the left and right said any moves to approve a Leopard tank upgrade deal should be halted.

The row could hinder the attempts of the two countries' foreign ministers to improve bilateral ties which have severely soured in recent years over matters including Turkey’s perceived slide into authoritarianism.

Germany was last week reportedly moving to approve a request from fellow Nato member Turkey for German arms manufacturer Rheinmetall to upgrade its Leopard 2 tanks, to make them less vulnerable to explosives, the BBC reported.

Defence experts have claimed in German media that recent images from Turkey's Operation Olive Branch appear to show Leopard tanks being used against Kurdish groups.

Norbert Röttgen, a member of Chancellor Angela Merkel's Christian Democratic Union (CDU) party and chairman of the parliamentary foreign affairs committee, said it was "completely obvious" that Germany should not provide the upgrades. He told BBC Radio 4's World Tonight programme that the intervention by Turkish forces was "illegal, contrary to international law and counter-productive with regard to fighting ISIS".

He added that Turkey could not claim to be acting in self-defence because "there have not been any attacks on Turkey by Kurdish forces in Syria".