The speaker of Russia's parliament warned Sunday that countries supplying Ukraine with more powerful weapons risked their own destruction, a message that followed new pledges of armored vehicles, air defense systems and other equipment but not the battle tanks Kyiv requested. "Supplies of offensive weapons to the Kyiv regime would lead to a global catastrophe," State Duma Chairman Vyacheslav Volodin said. "If Washington and NATO supply weapons that would be used for striking peaceful cities and making attempts to seize our territory as they threaten to do, it would trigger a retaliation with more powerful weapons." Ukraine's supporters pledged billions of dollars in military aid to Ukraine on Friday, though the new commitments were overshadowed by defense leaders failing at an international meeting in Ramstein, Germany, to agree on Ukraine's urgent request for German-made Leopard 2 battle tanks. Germany is one of the main donors of weapons to Ukraine, and it ordered a review of its Leopard 2 stocks in preparation for a possible green light. Nonetheless, the government in Berlin has shown caution at each step of increasing its commitments to Ukraine, a hesitancy seen as rooted in its history and political culture. Its tentativeness has drawn heavy criticism, particularly from Poland and the Baltic states, countries on NATO's eastern flank controlled by Moscow in the past and feel especially threatened by Russia's renewed imperial ambitions. Polish Prime Minister Mateusz Morawiecki said that if Germany does not consent to transferring Leopard tanks to Ukraine, his country was prepared to build a coalition of countries that would send theirs anyway. "Almost a year had passed since the outbreak of war," Morawiecki said in an interview with Polish state news agency PAP published Sunday. "Evidence of the Russian army’s war crimes can be seen on television and on YouTube. What more does Germany need to open its eyes and start to act in line with the potential of the German state?" "Above all, Berlin should not weaken or sabotage the activities of other countries," Morawiecki said. In Washington, two leading lawmakers urged the US on Sunday to send some of its Abrams tanks to Ukraine, in the interests of overcoming Germany’s reluctance to share its own, more suitable Leopard 2 tanks. "If we announced we were giving an Abrams tank, just one, that would unleash" the flow of tanks from Germany, Rep. Michael McCaul, the Republican chairman of the House Foreign Affairs Committee, told ABC’s "This Week on Sunday." "What I hear is that Germany’s waiting on us to take the lead." Dmitry Medvedev, the deputy head of the Russian Security Council, said the meeting in Ramstein "left no doubt that our enemies will try to exhaust or better destroy us," adding that "they have enough weapons" to achieve the purpose. Medvedev, a former Russian president, warned on his messaging app channel that Russia could seek to form a military alliance with foes of the United States. He didn’t name the nations he had in mind, but Russia has defense cooperation with Iran and Venezuela, an existing military alliance with Belarus and strong ties with North Korea. Since invading Ukraine, Russia also has increased both the scope and the number of its joint military drills with China. Ukraine is asking for more weapons as it anticipates Russia's forces launching a new offensive in the spring. Oleksii Danilov, the secretary of Ukraine’s Security and Defense Council, warned that Russia may try to intensify its attacks in the south and in the east and to cut supply channels of Western weapons, while conquering Kyiv "remains the main dream" in President Vladimir Putin’s "fantasies," he said. He described the Kremlin’s goal in the conflict as a "total and absolute genocide, a total war of destruction." "Moscow wants to completely destroy Ukraine as a historical phenomenon — its language, history, culture, carriers of Ukrainian identity," Danilov wrote in a column published by Ukrainska Pravda. Among those calling for more arms for Ukraine was the former British prime minister, Boris Johnson, who made a surprise trip to Ukraine on Sunday. "This is the moment to double down and to give the Ukrainians all the tools they need to finish the job. The sooner Putin fails, the better for Ukraine and for the whole world," Johnson said in a statement. Johnson, who faces fresh questions at home over his personal finances, was pictured in the Kyiv region town of Borodyanka. He said he traveled to Ukraine at the invitation of President Volodymyr Zelenskyy. The last week was especially tragic for Ukraine even by the standards of a brutal war that has gone on for nearly a year, killing tens of thousands of people, uprooting millions more and creating vast destruction of Ukrainian cities. A barrage of Russian missiles struck an apartment complex in the southeastern city of Dnipro on Jan. 14, killing at least 45 civilians, including six children. On Wednesday, a government helicopter carrying the interior minister and other officials crashed into a building housing a kindergarten in a suburb of Kyiv. The minister and a child on the ground were among the 14 people killed. Zelenskyy, who on Saturday mourned the victims of the helicopter crash, vowed Sunday that Ukraine would prevail in the war. "We are united because we are strong. We are strong because we are united," the Ukrainian leader said in a video address as he marked Ukraine Unity Day, which commemorates the day in 1919 when East and West Ukraine were united. "Dear invincible people, Happy Ukrainian Unity Day!" he said.