When asked about whether Berlin would make a new commitment to supply arms to Kyiv at the summit, the official, who spoke on condition of anonymity, said "yes... substantial. Very substantial".

The source did not provide further details ahead of the summit beginning Tuesday in Vilnius and set to be dominated by the alliance's response to Russia's war on Ukraine and Kyiv's push for NATO membership.

Echoing the reticence of other major partners, the German official said the summit would not deliver a membership "invitation" to Ukraine, underlining a preference in Berlin for "specific aid" and not "symbols".

But leaders are expected to agree to hold meetings between NATO and Ukraine "four times per year" to allow "improvement and a substantial intensification" of ties.

Since Russia invaded Ukraine in February last year, Germany has dropped a traditionally pacifist stance and sent a vast array of weaponry to Kyiv, from air defence to artillery systems. It is now Ukraine's second largest arms supplier after the United States.

Berlin earlier this year started sending advanced Leopard battle tanks to Ukraine, after months of pleas from Kyiv for the heavy weapons to bolster its fightback against Russia.

The government has so far delivered 18 of the advanced Leopard 2 tanks to Ukraine.

Russia earlier this month said that it had captured several Leopard tanks and US Bradley infantry fighting vehicles, releasing footage showing Russian troops surveying the equipment.

Ukrainian and German politicians have been calling for rapid resupply of tanks given the destruction of the armaments.

Meanwhile Defence Minister Boris Pistorius said Berlin would continue to supply the less advanced Leopard 1 tanks, and there would be over 100 by the end of the year.