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She said Germany would only have a direct role in the conflict if it sent troops into battle, rather than giving lessons to Ukrainian gunners on how to use German-made PzH 2000 howitzers.
Russian Foreign Minister Sergey Lavrov last month hinted at a potential nuclear conflict by suggesting Nato was effectively “engaged in a war with Russia through a proxy and is arming that proxy”.
Nato says it is determined to avoid falling into this trap and has resisted Ukraine’s pleas for a no-fly zone that might involve western planes shooting down Russian pilots.
But a panel of advisers to the German parliament suggested, in a report written in March and recently leaked to media outlets, that a line might be crossed if Ukrainians received training in Germany – something that is now set to take place.
The self-propelled PzH 2000 howitzers were offered to Ukraine by the Dutch military, but are of German design. The training for experienced Ukrainian gunners is due to take place at an artillery school in Idar-Oberstein, western Germany.
Eberhard Zorn, the chief of Germany's armed forces, said the country was also looking at what ammunition it could provide from its own stocks and considering whether it had any howitzers spare.
If such weapons shipments are accompanied by “instruction for the warring party or training in the use of such weapons … you would leave the safe territory of being a non-belligerent", the panel of experts wrote in a 12-page legal analysis.
The advisers said another grey area would be passing intelligence information on to Ukraine or briefing it on reconnaissance patrols carried out on Nato’s eastern flank.
They said Russian retaliation against one Nato member would drag the whole alliance into the conflict because of its so-called Article 5 commitment to treat an attack on one as an attack on all.
Ukraine is not a member of Nato.
But Ms Lambrecht played down such concerns during a visit to an air force base in Wunstorf, northern Germany, where she said Berlin remained a non-belligerent party.
“I don’t share the assessment that the training of Ukrainian soldiers here in Germany makes us a party to the war,” she said.
“I’m working on the basis that neither this training nor the delivery of weapons have that effect.
“If we sent soldiers into Ukraine, that would be a very clear signal. But we’re not going to do that. That’s not going to happen.”
It touches on a contentious issue in German politics. Chancellor Olaf Scholz is accused by the opposition of being too timid in his support of Ukraine, especially as far as weapons shipments are concerned, for fear of antagonising Moscow.
Mr Scholz has spoken of preventing an escalation that would lead to a nuclear conflict or a Third World War, but his government has moved to step up military aid to Ukraine in recent days owing to pressure from MPs.
Mr Zorn said the training was needed because the PzH 2000 was high-tech equipment that was “not comparable with typical howitzers that have so far been used in Ukraine”.
Germany has also offered Ukraine a supply of Gepard anti-aircraft tanks, whose 35 millimetre cannon can hit targets at an altitude of up to 5,500 metres.
An open letter from 28 self-described intellectuals and artists urged Mr Scholz to stick to his original position and said Nato countries would have a share of the responsibility if the conflict escalated.
But the letter was criticised by numerous politicians who said it was naive to think that appeasing Russia would eliminate the risk of a wider war.