President Biden on Friday urged Germany and other Western allies not to waver in their support for Ukraine, using what may be his final trip to Europe as president to bolster the grueling fight against Russia’s invasion.

“German leaders had the wisdom to recognize a turning point in history, an assault on a fellow democracy, and also on principles that upheld 75 years of peace and security in Europe,” Mr. Biden said after receiving Germany’s highest honor during a ceremony at the Bellevue Palace in Berlin.

Mr. Biden added that the allies must continue to work tirelessly to “ensure that Ukraine prevails and Putin fails and NATO remains strong and more united than ever.”

“We’re headed into a very difficult winter,” he added. “We cannot let up. We cannot.”

The honor Mr. Biden received was Germany’s grand cross special class of the order of merit, which is only awarded to heads of state.

When Mr. Biden planned this one-day trip to Germany, the purpose seemed clear. Washington and Berlin would showcase their cooperation, particularly on helping Ukraine in its fight against Russia’s aggression.

But Israel’s killing of Yahya Sinwar, the leader of Hamas, appeared likely to intrude on the agenda. Prime Minister Benjamin Netanyahu of Israel announced Mr. Sinwar’s death on Thursday, calling it “an important milestone in the sunset of Hamas’s evil rule in Gaza.”