“In recent months, NATO allies have not provided the support we promised,” he said in a speech during a visit to Berlin.
“However, it is not too late for Ukraine to win because support is on the way,” he added.
Kyiv has been weakened by shortages of ammunition and weapons in recent weeks.
But Mr. Stoltenberg stressed that the US Congress had finally approved a bill for billions of dollars in aid to Ukraine, and other countries, including the United Kingdom, Germany and the Netherlands, had also pledged new things.
“It is now our responsibility to translate these commitments into actual deliveries of arms and ammunition, and to do so quickly,” he said.
Mr Stoltenberg also attacked China, accusing Beijing of “supporting Russia’s war economy” by sharing cutting-edge technology that can be used to build missiles, tanks and planes.
“China says it wants good relations with Western countries. At the same time, Beijing continues to fuel Europe’s biggest armed conflict since World War II,” he said, warning that “they cannot be on both sides.”
Berlin and Beijing have traditionally maintained close economic ties, with German companies investing huge sums in China and exporting large quantities of goods to the world’s second largest economy.
But after the war in Ukraine caused an energy shock that hit Germany’s most important manufacturers particularly hard. German companies are under increasing pressure to reduce their dependence on authoritarian China.
However, Chancellor Olaf Scholz, who visited China last week, emphasized on Wednesday that Germany does not want to separate from China, but seeks to reduce its unilateral dependence.
