Stoltenberg said this in an interview with Reuters following his Kyiv visit, Ukrinform reports.
In his opinion, such "failings" indicate the need to revamp the coordination of international military aid to Kyiv.
"We need a more robust, institutionalized framework for our support to ensure predictability, to ensure more accountability and to ensure burden-sharing," Stoltenberg said.
Read also: Zelensky, Stoltenberg meet with officers undergoing NATO-standard training coursesAs an example of allies falling short, he cited the six-month delay by the U.S. Congress taking six months to approve a $60-billion aid package to Ukraine, as well as European countries delivering much less artillery ammunition than promised.
These shortcomings had a serious impact on the battlefield as Russia gained the initiative while Ukrainian forces, short on ammunition, were forced to go on the defensive, Stoltenberg noted.
"Of course, the fact that we have not delivered what we promised has put a dent … into trust," he emphasized.