Russia's assault on Ukraine has prompted world leaders to look, once again, at global threats to security. They have gathered in Germany to focus on the war and on how to avoid an "unwanted escalation."

Hundreds of participants are taking part in the Munich Security Conference starting Friday. The conference began in the 1960s as a forum for leaders to discuss crises by allowing even adversaries, and those from authoritarian nations, to join. But this time, no officials from Russia have been invited.

German Chancellor Olaf Scholz said, "We should carefully weigh all the consequences of our actions and closely consult on all important steps with our allies, because this war is close to us in Europe -- this dangerous war."

Scholz says allies should prepare for a long struggle and let Russian President Vladimir Putin know they will not back down.

Leaders in Kyiv say Russian forces have ambitions beyond Ukraine. President Volodymyr Zelenskyy warned that, if the allies do not show unity, Putin will go on to "consume" other states. He urged them to speed up delivery of weapons and make important decisions to "limit Russia's potential."

Participants will hold talks throughout the weekend. Asian leaders include Japan's Foreign Minister Hayashi Yoshimasa and China's top foreign policy official, Wang Yi. The US delegation is led by Vice President Kamala Harris. She is joined by nearly a third of all lawmakers from the Senate, as a show of bipartisan support for Ukraine.