Germany faced mounting pressure to supply battle tanks to Kyiv and Ukrainian President Volodymyr Zelenskyy aired frustration about not obtaining enough weaponry as Western allies conferred Thursday on how best to support Ukraine nearly 11 months into Russia’s invasion.

Just hours into his tenure, Germany’s new defense minister, Boris Pistorius, welcomed U.S. Defense Secretary Lloyd Austin to Berlin. He declared that German weapons systems delivered so far have proven their worth and that “we will continue in the future, together with our partners, to support Ukraine in its fight for freedom, territorial independence and sovereignty.”

He didn’t, however, mention the Leopard 2 tanks that Ukraine has long sought. Since the United Kingdom announced last week that it will send Challenger 2 tanks, Berlin has faced increasing pressure to supply battle tanks or at least clear the way for others — such as Poland — to deliver German-made Leopards from their own stock.

Austin is to host a regular coordination meeting of top defense officials from Ukraine’s Western allies at the United States’ Ramstein Air Base in Germany on Friday. He said that “we’ll renew our united commitment to support Ukraine’s self-defense for the long haul,” but didn’t mention any specific new equipment.

Speaking by video link to a breakfast meeting on the sidelines of the World Economic Forum’s annual meeting in Davos, Switzerland, Zelenskyy offered a veiled critique of major supporters such as Germany and the United States that have nonetheless hesitated about sending tanks.

He bemoaned a “lack of specific weaponry” and said that to win the war, “we cannot just do it with motivation and morale.”

Speaking at the Victor Pinchuk Foundation breakfast through an interpreter, he said: “There are times where we shouldn’t hesitate or we shouldn’t compare when someone says, ‘I will give tanks if someone else will also share his tanks.’”

Ukraine’s foreign and defense ministers said in a joint statement that the Challenger 2 tanks Britain plans to supply, while welcome, are “not sufficient to achieve operational goals.”

“We guarantee that we will use these weapons responsibly and exclusively for the purposes of protecting the territorial integrity of Ukraine within internationally recognized borders,” Dmytro Kuleba and Oleksii Reznikov said in an appeal to Germany and several other countries that use the German-made Leopard 2 to join an “international tank coalition.”

For months, Ukraine has sought to be supplied with heavier vehicles such as the Leopard and U.S. Abrams tanks, but Western leaders have been treading carefully.

Germany has been particularly in focus in recent days. Critics, some inside Germany’s governing coalition, have long complained of Chancellor OIaf Scholz’s perceived hesitancy to take the next step when it comes to weapons deliveries.

Scholz has been wary of such pressure, insisting that Germany wouldn’t go it alone and pointing to a need to ensure that NATO doesn’t become a party to the war with Russia, though every time so far Berlin has eventually moved ahead. He has portrayed his cautious weighing of each step as a virtue.

In Davos on Wednesday, Scholz avoided directly answering a question about Leopard tanks, saying that Germany will remain one of Ukraine’s top weapons suppliers and that “we are never doing something just by ourselves, but together with others — especially the United States.”

German officials have conveyed their hesitancy to allow allies to give German-made Leopards unless the U.S. also sends Ukraine the Abrams, according to a U.S. official who was not authorized to comment and spoke on the condition of anonymity. An upcoming new package of U.S. military aid is expected to include nearly 100 Stryker combat vehicles and at least 50 Bradley armored vehicles — but not the Abrams, which U.S. officials says has complex maintenance needs and may not be the best fit.

Austin said on Twitter that he plans also to meet Scholz’s chief of staff, Wolfgang Schmidt, while in Berlin.

“I think this isn’t about avoiding going it alone any more, but about avoiding being alone,” Wolfgang Ischinger, a former German ambassador to the U.S., said on Deutschlandfunk radio of the calls for German tank deliveries.

Some eastern NATO allies have provided Soviet-era T-72 tanks to Ukrainian forces, but officials acknowledge that supplies of Soviet-era equipment with which Ukrainian forces were already familiar are limited.

NATO Secretary-General Jens Stoltenberg said Ukraine’s Western backers this week will discuss ways to supply heavier and more advanced weapons.

“The main message there will be: more support, more advanced support, heavier weapons and more modern weapons,” Stoltenberg said of Friday’s meeting.

Defense ministers from Britain, Poland and the Baltic nations were to meet on Thursday afternoon in Estonia ahead of that gathering.

Swedish Prime Minister Ulf Kristersson said Thursday that his country has decided to send up to 50 Swedish-made combat vehicles plus a shoulder-fired anti-tank missile system and the Archer artillery system to Ukraine.