NATO Secretary General Jens Stoltenberg urged allies on Tuesday to speed up deliveries of heavy and more advanced weapons to repel Russian forces in Ukraine and expressed confidence that a decision on sending battle tanks to Kyiv would come soon.

Stoltenberg was speaking in Berlin alongside Germany's new defense minister, Boris Pistorius, who said his government would act quickly on the tanks if a consensus was found.

Pressure has been building on German Chancellor Olaf Scholz's government to send its Leopard tanks to Ukraine and also let other countries send the ones they own – under military procurement rules, Germany must authorize any re-exports.

But Scholz's Social Democrat party has been holding back, wary of sudden moves that could cause Moscow to escalate further.

A German defense source told Reuters that Poland had submitted a request to the German government to let it supply up to 14 Leopard 2 A4 tanks to Ukraine, upping the pressure on Berlin still further.

Earlier, Polish Defence Minister Mariusz Blaszczak urged Germany to give the go-ahead over the heavy armor. "This is our common cause, because the security of the whole of Europe is at stake!" he wrote on Twitter.

"At this pivotal moment in the war, we must provide heavier and more advanced systems to Ukraine, and we must do it faster," NATO's Stoltenberg told reporters.

"I therefore welcome our discussion today. We discussed the issue of battle tanks. Consultations among allies will continue and I'm confident we will have a solution soon," Stoltenberg added.

Pistorius said Germany was not standing in the way of other countries training Ukrainian troops to use the Leopard tanks while talks continued. He said it was wrong to say that "there's disunity or that Germany is isolated."

Scholz was trying to forge consensus on the tanks issue, he said, adding that NATO must not become party to the war in Ukraine.

The decision about the delivery of the tanks would be taken solely at the political level, German defense chief Eberhard Zorn said at a conference in Berlin organized by Handelsblatt.

Germany's foreign minister Annalena Baerbock had signaled a possible breakthrough on Sunday when she said her government would not stand in the way if Poland wants to send its Leopard 2 tanks to Ukraine.

But on Tuesday a German foreign ministry official appeared to temper those remarks by saying that Scholz would decide on sending the tanks.