President Volodymyr Zelensky of Ukraine made a passionate appeal by video on Wednesday to heads of state and other decision makers gathered at the World Economic Forum in Davos, Switzerland, urging a faster pace of support for his country in the face of Russia’s invasion.

At the start of Mr. Zelensky’s address, which he delivered in English, he called for a minute of silence to honor Ukraine’s minister of internal affairs, Denys Monastyrsky, and more than a dozen others who were killed in a helicopter crash near Kyiv, Ukraine’s capital, earlier on Wednesday. He called the crash, whose cause is being investigated, a tragedy and another example of the unnecessary deaths that have marked the conflict.

Too often, he said, Ukraine found itself racing against time. “Tragedies are outpacing life. The tyranny is outpacing democracy,” Mr. Zelensky said. “The time the free world uses to think is used by the terrorist state to kill.”

It had taken only seconds for Russian tanks to roll across the border last February, Mr. Zelensky said, but days before sanctions were imposed. A Russian missile, he said, traveled across the country in minutes before striking a building in the city of Dnipro on Saturday, killing 45 people.

“The supplying of Ukraine with air defense systems must outpace Russia’s next missile attacks,” he said. “The supplies of Western tanks must outpace the next invasion of Russian tanks.”

Mr. Zelensky has pressed his country’s case before many international groups, including the United Nations General Assembly, Congress, the European Parliament and the Group of 20 nations. Only the address to Congress was made in person.

Others are also making appeals for Ukraine at Davos. The country’s first lady, Olena Zelenska, spoke on Monday, and Vitali Klitschko, the mayor of Kyiv, is there with his brother, Wladimir Klitschko, a fellow former heavyweight boxing champion.

Mr. Zelensky has repeatedly argued that Moscow felt empowered to invade Ukraine in part because of the limited international response to Russia’s invasion in 2014, during which it annexed the Crimean Peninsula and set up two breakaway republics in the eastern region of Donbas. On Wednesday, he sought to set the war in the context of a struggle for democratic values.

“We routinely defend values that some of our allies take for granted as a fact of life,” he said. “At first the world underestimates a threat, then it unites to resist it, and then the world wins.”

Mr. Zelensky spoke during a critical week of diplomacy, as Ukraine pushes for more advanced arms including tanks and air defense missiles. On Tuesday, the Netherlands said that it intended to follow the United States and Germany by sending a Patriot missile system to Ukraine. The same day, General Mark A. Milley, the chairman of the U.S. Joint Chiefs of Staff, spoke with his Ukrainian counterpart in Poland, their first face-to-face meeting since Russia’s invasion last February.

On Wednesday, NATO defense ministers began a two-day meeting in Brussels to assess aid for Ukraine. On Friday, they will be at Ramstein Air Base in Germany, joined by officials from a broader group of nations coordinating the assistance. The U.S. defense secretary, Lloyd J. Austin III, will lead those discussions, which will include the crucial issue of sending Western tanks.