Ukrainian authorities on Thursday were investigating the circumstances surrounding a helicopter crash that killed the country's interior minister and 13 others.
Wednesday's crash outside Kyiv came as the head of NATO said at the annual World Economic Forum in Davos that allies were set to provide "heavier weapons" to the war-battered country.
Ukraine did not claim direct Russian involvement in the helicopter crash, but President Volodymyr Zelensky said the tragedy was a consequence of the war.
"There are no accidents at war. These are all war results," Zelensky said in English, appearing by video link at Davos.
He also renewed calls for modern, Western-designed heavy tanks, which analysts say are crucial to pushing through entrenched defensive lines in eastern Ukraine.
In a barely veiled reference to Germany, where Chancellor Olaf Scholz is weighing whether to green light the export of its highly regarded Leopard tanks, Zelensky issued a "call for speed".
"The time the Free World uses to think is used by the terrorist state to kill," Zelensky told delegates in Davos.
The statement came after NATO chief Jens Stoltenberg said the alliance would provide "more advanced support, heavier weapons and more modern weapons, because this is a fight for our values".
Meanwhile, in Washington, Under Secretary of Defense for Policy Colin Kahl said the United States was not "there yet" when it came to providing advanced Abrams tanks to Ukraine, though he did not completely close the door on a shift in the future.
